UV effects on Skin

25 Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub. 2006, 150(1):25–38.
© A. Svobodova, D. Walterova, J. Vostalova
ULTRAVIOLET LIGHT INDUCED ALTERATION TO THE SKIN
Alena Svobodova*, Daniela Walterova, Jitka Vostalova
Institute of Medical Chemistry and Biochemistry, Faculty of Medicine, Palacký University, Hněvotínská 3, 775 15 Olomouc,
Czech Republic;
e-mail: [email protected]
Received: April 28, 2006; Accepted: May 15, 2006
Key words: UV radiation/Skin/DNA damage/Reactive oxygen species (ROS)/p53/Antioxidant enzymes
Solar light is the primary source of UV radiation for all living systems. UV photons can mediate damage through
two different mechanisms, either by direct absorption of UV via cellular chromophores, resulting in excited states
formation and subsequent chemical reaction, or by phosensitization mechanisms, where the UV light is absorbed by
endogenous (or exogenous) sensitizers that are excited and their further reactions lead to formation of reactive oxygen
species (ROS). These highly reactive species can interact with cellular macromolecules such as DNA, proteins, fatty
acids and saccharides causing oxidative damage. Direct and indirect injuries result in a number of harmful effects
such as disrupted cell metabolism, morphological and ultrastructural changes, attack on the regulation pathways and,
alterations in the differentiation, proliferation and apoptosis of skin cells. Processes like these can lead to erythema,
sunburn, inflammation, immunosuppression, photoaging, gene mutation, and development of cutaneous malignancies.
The endogenous and exogenous mechanisms of skin photoprotection are discussed.
INTRODUCTION
Ultraviolet (UV) radiation has a few beneficial health
effects like vitamin D
3
formation or application in combi-
nation with drugs in the therapy of skin diseases including
psoriasis and vitiligo, but it also causes many acute and
chronic detrimental cutaneous effects, which may result
in development of skin malignancies. Among all human
cancers, skin cancer is currently one of the most common
types. The incidence of both melanoma and non-melano-
ma skin cancers (basal cell carcinoma (BCC) and squa-
mous cell carcinoma (SCC)), the serious consequence of
UV action, is still increasing worldwide
1
.
Sunlight is composed of a continuous spectrum of
electromagnetic radiation that is divided into three main
parts of wavelengths: ultraviolet (45 %), visible (5 %),
and infrared (50 %). UV light region occurs between
100–400 nm (Fig. 1). According to the International
Commission on Illumination, UV radiation is divided into
three categories depending on the wavelength: long wave
UVA (315–400 nm), medium wave UVB (280–315 nm),
and short wave UVC (100–280 nm)
2–4
.

The ozone layer
efficiently absorbs UV radiation up to about 310 nm thus
it consumes all UVC and most of UVB (95 %). However,
UVA is not absorbed at all
5
. Due to substantial damage to
the protective ozone layer an increased amount of UVB
radiation is reaching the ground
4
.
UVA comprises more than 95 % of solar radiation that
reaches us. Compared to UVB, this long wave radiation
penetrates deep into the epidermis and dermis of the skin
and is about 1000 times more effective in the production
of an immediate tanning effect, which is caused by darken-
ing of the melanin in the epidermis
3
. Intense or extensive
exposure to UVA can burn sensitive skin, and if pro-
longed, it can damage underlying structures in the corium
and cause premature photoaging of the skin. More or less
early signs of photoaging include wrinkling, wilting, laxity,
sagging, patchy pigmentation, dryness etc. UVA injury
Fig. 1. Solar radiation spectrum.
26 A. Svobodova, D. Walterova, J. Vostalova
also causes necrosis of endothelial cells, thus damaging
the dermal blood vessels. UVA-induced responses in cells
happen mainly indirectly via oxidative processes initiated
by endogenous photosensitization. After UVA exposure,
reactive oxygen species (ROS) are generated and can me-
diat damage to cellular proteins, lipids, and saccharides.
UVA can produce structural damage to DNA, impair the
immune system, and lead to cancer. It has been linked to
67 % of malignant melanoma
3, 6–8
.
UVB radiation is a minor but the most active constitu-
ent of solar light. It makes up 4 to 5% of coming UV light.
It is most intense from 11:00 a.m. to 1:00 p.m. all year
long. It is more genotoxic and about 1000 times more ca-
pable of causing sunburn than UVA. UVB is less penetrat-
ing and acts mainly in the epidermal basal cell layer of the
skin. It induces particularly, direct damage to DNA (the
formation of cyclobutane-pyrimidine dimers (CDPs) and
pyrimidine-pyrimidone (6-4) photoproducts ((6-4)-PP))
and proteins (interaction with aromatic amino acids).
UVB also participates in indirect damage to macromol-
ecules. It provokes free radical production and induces a
significant decrease in skin antioxidants, impairing the
skin’s ability to protect itself against the free radicals gen-
erated after sunlight exposure. Furthermore, UVB causes
photoisomerization of trans- to cis-urocanic acid (UCA),
induction of ornithine decarboxylase (ODC) activity and
cell cycle arrest, or impairment of DNA synthesis in the
skin. Both direct and indirect adverse biological effects of
UVB may result in photoaging and photocarcinogenesis.
UVB is considered to be responsible for inducing BCC
and SCC due to DNA damage. It is also suspected of
lowering the skin’s immune defence system
6–11
.
The UVC light is the most energetic and has the great-
est potential for biological damage to all forms of life, even
with only very short exposures. It is highly mutagenic and
toxic. It is absorbed by proteins and nucleic acids and is
extremely damaging to the skin. Fortunately, UVC radia-
tion from the sun is completely absorbed in the earth’s
atmosphere. In the stratosphere the UVC energy is uti-
lized to form ozone from the molecular oxygen and no
solar radiation of wavelengths below 280 nm reaches the
surface of the earth
2, 6, 7, 12
.
UV-induced skin injury depends on many variables
including wavelength, dose, race, and characteristics of
the skin tissue
13
. While UVB is maximal between 11 a m.–
1 p. m., UVA still makes up to 50–60 % of the photo-
toxic wavelength, and this is increased at other times
3
.
Obtainable UV dose increases with an increasing altitude
and decreasing latitude and also changes with the season
(Tab. 1). Most indoor-working adult Europeans get 10–
20 kJ.m
–2
per year, Americans 20–30 kJ.m
–2
per year and
Australians 20–50 kJ.m
–2
per year. Holidays can increase
the dose by 30 % or more. Outdoor-working people get
about 2.5–5 times higher UV dose than indoor-working
ones that represent 10 % of the total available annual UV
amount
14
. Individual genetic sensitivity is also an impor-
tant determinant of the susceptibility to UV radiation
13
.
MECHANISMS OF UV-INDUCED BIOLOGICAL
DAMAGE
To exert its biological effects, UV light energetic pho-
tons must be first transmitted through skin layers and
absorbed by a cellular molecule (chromophore, photosen-
sitizer). Then series of biological reactions are initiated.
UV radiation induces damage via two different mecha-
nisms. One is direct absorption of UV photons by cellular
chromophores that can lead to photo-induced reactions.
This kind of injury is typical for DNA bases. The sec-
ond, indirect way, include photosensitization processes,
where endogenous or exogenous sensitizers absorb UV
light
10
. Absorbing the energy of the photons changes the
distribution of electrons in the chromophores/photosen-
sitizer molecule and creates the excited singlet state. In
this state, the molecule can emit fluorescence, lose the
energy as heat, undergo a photochemical reaction to form
photoproducts, or change into the triplet excited state. In
this long-lived state, the molecule emits phosphorescence,
photochemically reacts (Fig. 2), or returns to the ground
state
10, 15
. Subsequent photobiochemical reactions, depend-
ing upon the epidermal thickness, the concentration and
the distribution of chromophores, provoke changes in cell
and tissue biology
3, 8
.
Cellular damage via an excited photosensitizer may
occur by two major pathways often called Type I and
Table 1. Solar irradiance measurement during the sea-
sons (taken form ref
14
).
Spring Summer Autumn Winter
3/27 6/30 9/27 12/20
UVB (mW/cm
2
) 0.211 0.243 0.211 0.060
UVA (mW/cm
2
) 4.20 4.20 3.90 1.78
Ratio UVA/UVB 19.9 17.3 18.5 29.7
UVB (J/cm
2
) 4.26 6.19 4.51 1.19
UVA (J/cm
2
) 99.4 127.8 97.9 40.3
Ratio UVA/UVB 23.3 20.6 21.7 35.1
Solar noon measurements
Integral daily dose
Indolyl radical
3
Trp
N
.
HN
O
C.
N
HN
O
N
.
HN
O
O
O
.
O
2
Fig. 2. Reaction of tryptophane in triplet state induced
by UV radiation (taken from ref.
10
).
27 Ultraviolet light induced alteration to the skin
Type II. The mechanisms are dependent on the chemical
properties of photosenzitizers. Type I mechanisms involve
one electron transfer through a direct interaction between
an excited photosensitizer and other biomolecules, result-
ing in free radical formation. This mechanism does not
require oxygen for the induction of molecule damage. The
Type II mechanism involves energy transfer from an ex-
cited sensitizer to molecular oxygen that leads to produc-
tion of reactive oxygen species (ROS) (Fig. 3). Mostly
singlet oxygen, an excited state of oxygen, which is a very
powerful oxidant with relatively long lifetime, is gener-
ated. However, in minority reactions superoxide anion
is also produced, followed by dismutation to hydrogen
peroxide
10
. Hydrogen peroxide is not capable of causing
damage by itself, but in the presence of metal cations (Fe,
Cu) hydroxyl radicals are generated by the Fenton reac-
tion. ROS interactions with cellular biomolecules provoke
a final biological response (Fig. 4) (ref.
16
).
UV ABSORBING CELLULAR CHROMOPHORES
Numerous biomolecules in the skin act as radiation
absorbents within the UVB range. These are mainly nu-
cleic acids, aromatic amino acids, NADH and NADPH,
heme, quinones, flavins, porphyrins, carotenoids, 7-de-
hydrocholesterol, eumelanin and urocanic acid (UCA)
(ref.
2, 3, 8, 13, 17
).

UVA-absorbing cellular molecules in the
initiation of UVA-induced photosensitization are still
largely unknown, only trans-UCA and melanin have been
reported
8
.
The major chromophoric amino acids present in pro-
teins are tryptophane, tyrosine, phenylalanine, histidine,
and cysteine. The absorption of UV light by these amino
acids can give both excited state species and radicals via
photo-oxidation (Fig. 2) (ref.
10
).
UCA, a histidine derivative, is a major UV absorbing
chromophores in the stratum corneum of human skin.
UV radiation provokes the isomerization of trans-UCA to
cis-UCA in a dose-dependent fashion until the stationary
state is reached when approximately equal quantities of
two isomers are present. The isomerization is maximal be-
tween 300–310 nm in human skin, although wavelengths
in the UVA range (315–400 nm) can also induce cis-UCA
formation
4,18
.
Melanin acts as a filter by absorbing UVB, UVA, vis-
ible and IR radiation, helps transforming this energy into
heat, and disperses it between hairs and capillary vessels.
It efficiently scavenges OH· and molecular oxygen and
preserves the DNA from photoproduct formation. On
the other hand, melanin precursors are inherently cyto-
toxic to the melanocytes. For example, autooxidation of
dihydroxyphenylalanine and indolic precursors may give
arise to cytotoxic oxygen species. One of these products
dihydroxyindol, being similar to the purine bases, can re-
act with DNA by inserting itself between bases and may
act as a non-specific mutagen. UV radiation also enhances
binding of dihydroxyindol to DNA (ref.
2
).
Other macromolecules such as lipids and polysaccha-
rides do not absorb in the UV region and thus do not
undergo direct damage. Their disruption happens mainly
via oxidative proceses
10
.
EFFECT OF UV RADIATION ON CELLULAR
NUCLEIC ACIDS
In the skin, nucleic acids are the most critical chromo-
phores for UV radiation-induced biological response in
the UVB range. Fortunately, aromatic amino acids of pro-
teins in the stratum corneum, the most peripheral layer
of the skin, absorb large amount of UVB before it reaches
the nucleic acid molecules in the viable cells
2
. UVB light
was experimentally demonstrated to cause DNA damage,
mostly by formation of dimeric photoproducts between
H
2
O
2
O2
(A)
UV O2 R
Sen Sen* R
· +
+ Sen
· -
O
2
· -
+ Sen
(B)
UV O2
Sen* Sen
1
O
2
+ Sen
O
2
· -
+ Sen
· +
Me
+
HO
·
UVA
UVA UVA
UVC UVB UVA
UVC
UVC
UVB
UVA
Photosenzitizer
Immune
response
UVA UVB
Inflammation
DNA
damage
ROS
DNA
repair
Protein oxidation
Lipid oxidation
Antioxidant
defense
systems
Mutation
Multistep carcinogenesis
Apoptosis
O3
Fig. 3. Mechanisms of indirect UV-induced damage and
ROS formation.
Sen – photosensitizer, Sen* – Excited photosen-
sitizer, R – DNA base/aromatic amino acid (pro-
tein) Me
+
– metal cation
Fig. 4. Action of UV radiation on cellular biomolecules
(modified from ref.
23
).
28 A. Svobodova, D. Walterova, J. Vostalova
adjacent pyrimidine bases on the same strand (Fig. 5),
CPDs and (6-4)-PP. Upon exposure to UVB/A light, the
(6-4)-PP adducts are readily converted into Dewar valence
isomers (Fig. 5). These Dewar isomers are only moderate-
ly photoactive, but can undergo reversion to the (6-4)-PPs
upon exposure to short-wavelength UV radiation
10
.
Incorrect repair of these lesions leads to mutations
in the epidermal cells, which cause the development of
cancer cells. Among CPDs, thymine-cytosine (TC) and
cytosine-cytosine (CC) dimers are shown to be the most
mutagenic, since TC → TT and CC→TT mutations are
frequently found in the p53 gene of UV-induced cancer
cells
19
. (6-4)-PP are repaired more efficiently than CPDs
and for this reason CPDs are assumed to be the major
contributor to mutations in mammals
19, 20
.
One recent study suggests that UVA and UVB radia-
tion induce mutation via similar mechanisms. Differences
in the cellular responses to UVA and UVB, such as the
less prominent activation of p53 by UVA, might determine
a different mutagenic outcome of UVA- and UVB-induced
dimers. The authors speculate that the weaker activation
of p53 after UVA exposure, in comparison to the strong
activation of p53 after UVB, increases the chance that a
pyrimidone dimer leads to mutation formation, due to
weaker cell cycle arrest and a subsequent higher chance
of damaged template replication, due to less p53-mediated
induction of DNA repair. Furthermore, less p53-mediated
apoptosis might also increase the chance that cells with
damaged DNA or mutations will survive and potentially
progress to form skin cancer. If this hypothesis is true,
than UVA-induced dimers are more mutagenic due to less
pronounced protective DNA damage response
21
.
UV radiation also induces damage to RNA that can
lead to structural changes in expressed genes and causes
production of un-functional proteins
13
. Furthermore, a
blockade of RNA transcription that occurs as a result
of DNA photoproduct formation, leads to activation
of the p53 protein that induces apoptosis of irradiated
keratinocytes
3, 8
.
ROS-INDUCED SKIN DAMAGE
UV exposure to the skin results, among others events,
in generation of ROS (Fig. 3). These comprise a number
of active metabolites including OH·, O
2
·-
and peroxyl
radical and their active precursors namely
1
O
2
, H
2
O
2
and
ozone. Reactive nitrogen species (RNS), such as nitric
oxide (NO) and nitric dioxide, are also generated
22
. On
the other hand, ROS are natural and inseparable part of
metabolism. In skin, they are constantly generated in ke-
ratinocytes and fibroblasts, and are rapidly removed by
nonenzymic (ascorbic acid, tocopherol, ubiquinol, and
glutathione (GSH)) and enzymic antioxidants (catalase
(CAT), superoxide dismutase (SOD), thiredoxin reduct-
ase, glutathione peroxidase (GPx), and glutathione reduct-
cyclobutane-pyrimidine
dimer
UVB
HN
N
R
CH3
O
O
HN
N
R
H3C
O
O
H3C CH3
HN
N N
HN
R
O
O
R
O
O
A)
(6-4)-pyrimidine-pyrimidone
photoproduct
Dewar isomer
B)
UVB
HN
N
R
CH3
O
O
HN
N
R
CH3
O
O
CH3
OH
HN
N
R
O
O
UVB/A
UVB
O
CH3
OH
HN
N
O
O
H3C
R
N
N
O
H3C
R
N
N
Fig. 5. Formation of pyrimidine dimer from adjacent pyrimidine bases on the same strand (A), (6-4)-pyrimidine-
pyrimidone photoproduct and Dewar isomer (B) after absorption of UVB light energy (taken from ref.
10
).
29 Ultraviolet light induced alteration to the skin
ase) that maintain the pro-oxidant/antioxidant balance,
thus resulting in cell and tissue stabilization
22, 23
.
However, overflow of ROS, extensively formed by the
reaction of UV photons with endogenous photosensitizers
in the skin, may overwhelm the antioxidant (AOx) defence
mechanisms resulting in pro-oxidant/AOx disequilibrium
defined as oxidative stress
7,13
. UVA has a larger impact on
oxidative stress in the skin than UVB by inducing ROS/
RNS which damage DNA, proteins and lipids and which
also lead to NADH depletion, and therefore energy loss
from the cell
24
.
The excess of free radicals results in a cascade of
events mediating a progressive deterioration of a cellu-
lar structure and function, and this can lead to the dif-
ferentiation of neoplasic tissues
7
. It has been reported
that ROS/RNS induce various types of oxidative DNA
lesions that are thought to be important for the initiation
stage in carcinogenesis
25
. These highly reactive, short-lived
molecules produce single strand breaks, DNA-protein
crosslinks, and altered DNA bases. Due to low ionisa-
tion potential the guanine bases are the most susceptible
to oxidation via both Type I and Type II mechanisms.
Adenine is the second, followed by approximately equal
reactions for thymine and cytosine. The primary inter-
mediates generated by the Type I reaction are radical
cations, which undergo rapid hydration or deprotona-
tion. Hydration of the guanine radical cation produces a
reducing radical intermediate. Under reducing conditions
this radical is converted to 2,6-diamino-4-hydroxy-5-forma-
midoguanine, but under oxidizing conditions (e.g. in the
presence of molecular oxygen) it is converted to 8-oxo-
7,8-dihydro-2‘-deoxyguanine (8-oxo-dG). Deprotonation
of the guanine radical cation leads to series of reactions
generating a stable oxazolone product. The primary in-
termediates of Type II reactions, mediated by singlet
oxygen, are endoperoxides generated by cycloadition
reaction of the imidazole ring with singlet oxygen. The
major decomposition product of these endoperoxides is
8-oxo-dG (ref.
10
). Modified bases, particularly 8-oxo-dG,
are produced more frequently than single-strand breaks
or DNA-protein crosslinks by UVA (ref.
1
). 8-oxo-dG is a
characteristic mutagenic lesion (Fig. 6), which generates
GC → TA transversion by pairing with an adenine instead
of a cytosine during replication
1, 26
.
In addition to nuclear DNA, the DNA in mitochon-
dria may also be altered by UV-induced oxidative stress.
As DNA repair is less efficient in mitochondria compared
to nuclei, mutations accumulate at a relative rapid rate.
Identified mutations are deletions, which can be mediated
by UVA-induced
1
O
2
. These mutations may alter the cells
capacity to carry out oxidative phosphorylation
26
.
ROS also induce damage to cell membranes by per-
oxidation of fatty acids within the phospholipid structure
of the membrane. During this process, lipid peroxide
radicals, lipid hydroperoxides and other fragmentation
products, that are themselves active oxidizing agents, are
formed
23
. The lipid peroxides are comparatively longer-
lived species and can initiate the chain reactions that
enhance oxidative damage
16
. UVA-induced ROS also read-
ily react with membrane lipids and amino acids (Fig. 7).
ROS can modify proteins in the tissue to form carbonyl
derivatives (Fig. 8).
CHRONIC UV EFFECTS
Although the skin possesses an elaborate AOx system
to deal with the oxidative stress, extensive and chronic
exposure to UV, associated with abundant ROS/RNS gen-
eration, leads to oxidative damage that may result in skin
8-hydroxy-deoxyguanosine 8-hydroxy-deoxyadenosine
8-hydroxy-deoxycytosine thymine glycol
HN
N
N
N
dR
O
H2N
OH
H
N
N
N
N
dR
H2N
OH
H
HN
N
dR
CH3
O
OH
H
OH
HN
N
O
N
N
dR
OH
NH2
O
Fig. 6. The major DNA lesions produced by oxidative
damage (taken from ref.
20
).
dR – deoxyribose
3a-hydroxy-6-oxo-2,3,3a,6,7,7a-
hexahydro-1H-indol-2-carboxylic acid
N
O
HO
1
O
2
O
HO
N
OOH
O
HO
N
OH
H protein
protein
protein
H
Fig. 7. Singlet oxygen-mediated oxidation of tyrosine (taken from ref.
10
).
30 A. Svobodova, D. Walterova, J. Vostalova
disorders, inflammation, immunosuppression, premature
skin aging (photoaging) and carcinogenesis
27, 28
.
UVA is more important in causing skin inflammation
in humans than UVB (ref.
25
). However UVB participate in
the development of the cutaneous inflammatory response
as well
28
. The inflammation process includes a cascade of
events, which involves infiltration of inflammatory blood
leucocytes (macrophages and neutrophils), an increased
production of prostaglandins (PGs) as the consequence
of increased lipid peroxidation (LPx), a release of tumor
necrosis factor-alpha (TNF-α), nuclear factor-κB (NFκB),
inflammatory cytokines (interleukines; IL-1α, IL-1β, IL-
6), which further produce ROS and increase oxidative
stress. Inflammation also plays an important role in skin
cancer development
7
. Inflammation causes benign human
solar keratosis to undergo malignant conversion into SCC
probably because the inflammatory cells produce ROS,
thus increasing oxidative damage to DNA (ref.
24
). Both
UVB and UVA also suppress the human immune system.
According to studies, the UVA effect is very intricate and
shows a strong genetic dependence. Medium doses modu-
late immunity; higher doses can protect the immune sys-
tem from the suppressive effect of UVB, while lower doses
(below 840 mJ/cm
2
) of UVA can enhance the memory of
cell development
29
.
Photoaging includes a complex of biologic processes
affecting various layers of the skin with the major dam-
age seen in the cognitive tissue of the dermis
30
. This is
the result of the chronic sun exposure. The clinical symp-
toms include dryness, wrinkling, elastosis, telangiectasia,
and anomalous pigmentation. Histologically, the dermis
is strikingly filled with on amorphous mass of deranged
elastic fibers. Collagen fibers are desorganized. Blood
vessels are dilated and tortuous. Dermal inflammatory
cells are increased. Keratinocytes are irregular with loss
of polarity. Melanocytes are abnormal and decreased in
number
26
. Although UVB photons are much more ener-
getic than UVA, they are essentially completely absorbed
in the epidermis and are mostly responsible for sunburn,
suntanning and photocarcinogenesis. Thus UVA is sus-
pected to play a substantial role in photoaging
20, 26
. UVA-
induced matrix metalloproteinases (MMPs) are capable
of degrading the skin collagen framework at the same
time as procollagen synthesis is inhibited. MMP-1 cleaves
collagen type I, MMP-2 degrades elastin as well as base-
ment membrane compounds including collagen type IV
and VII, MMP-3 reveals the broadest substrate specificity
for proteins such as collagen type IV, proteoglycans, fi-
bronectin, and laminin
16, 26, 30
. Levels of procollagen I pro-
teins are decreased in the UV exposed skin. In addition,
NFκB activated by UV radiation, stimulates neutrophil
attraction bringing neutrophil collagenase (MMP-8) to
the irradiation site to further aggravate matrix degrada-
tion. Oxidative stress can also increase elastin mRNA
levels in dermal fibroblasts providing a mechanism for
the elastolytic changes found in the photoaged dermis.
Membrane lipid damage caused by UVA-induced ROS,
results in the release of arachidonic acid (AA) and this
leads to altered membrane fluidity and activation of sec-
ondary cytosolic and nuclear messengers that activate
UV-response genes
20, 26
. Human skin exposed daily for 1
month to sub-erythemic UVA dose demonstrated epider-
mal hyperplasia, stratum corneum thickening, Langerhans
cell depletion and dermal inflammatory infiltrates with
deposition of lysozymes on the elastic fibers
31
. These
changes suggest that even casual exposure to sunlight
while wearing a UVB-absorbing sunscreen may eventu-
ally result in damage to dermal collagen and elastin in
ways expected to produce photoaging
20
.
While acute UV radiation induces apoptosis involving
p53 and the Fas-Fas ligand pathway, chronic exposure
results in disruption of apoptosis regulation leading to
abnormal proliferation of keratinocytes containing dam-
aged DNA, accumulation of p53 mutations and loss of
Fas-Fas ligand interactions, all of which contribute to
carcinogenesis
1
.
UV-INDUCED EXPRESSION OF SKIN ENZYMES
In addition to macromolecule damage UVA/UVB-gen-
erated ROS also affect regulation of gene expression of
signalling molecules/cascades (Tab. 2) such as mitogen-
activated protein kinases (MAPKs) and interrelated
inflammatory cytokines as well as NF-κB and activator
protein-1 (AP-1). These may contribute to the induction
of heme oxygenase-1 (HO-1) and matrix metalloprotein-
ases (MMPs) in the skin. Increased levels of HO-1 may
P P
P
P P
C3-hydroperoxide
kynurenine N-formylkynurenine
Dioxetane
NH
O
O
HN
O
or
N
O
HN
O
OH
NH
OH
N
O
HN
NH
O
O
H
O
HN
NH
2
O
O
3α-hydroxypyrroloindole
Fig. 8. Products of singlet oxygen-mediated oxidation of tryptophane
(taken from ref.
10
).
31 Ultraviolet light induced alteration to the skin
elevate cellular levels of iron that can promote further
ROS generation.
Matrix metalloproteinases
Matrix metalloproteinases (MMPs; EC 3.4.24.X-Y)
are a family of zinc-dependent endopeptidases, which
are constantly produced by skin cells such as fibroblasts,
keratinocytes, macrophages, endothelial cells, mast cells,
and eosinophils. They can be induced temporarily in
response to exogenous signals including UV radiation
2
.
MMPs induction leads to enhanced degradation of the ex-
tracellular matrix proteins that favour wrinkle formation.
ROS inactivate tissue inhibitors of MMPs and induce the
synthesis and activation of matrix-degenerating MMPs.
Specific MMPs are induced by UVA trough
1
O
2
and H
2
O
2

(MMP-1, MMP-2, MMP-3, and MMP-9), whereas UVB
generated OH· and LPx induce MMP-1 and MMP-3 and
MMP-9 (ref.
8, 32
). The other pathway of UV-induced ex-
pression is due to activation of cell-surface receptors with
subsequent activation of MAPKs cascade or via expres-
sion of inflammatory cytokines
2
. The increased MMPs
synthesis can augment the biological aggressiveness of
skin cancer
26
.
Cyclooxygenases
Cyclooxygenases (COXs; EC 1.14.99.1), prostaglandin-
endoperoxide synthases, are enzymes that catalyse conver-
sion of AA to PGs. PGs are lipid signalling mediators that
play a central role in many normal and pathophysiological
processes including inflammation
33
. Of the two known
COX enzymes, COX-1 is constitutively expressed in nearly
all cells, whereas COX-2 is the inducible form
7
. Both UVA
and UVB parts have been shown to induce COX-2 protein
expression in skin
34
. The induction of COX-2 enzyme and
an elevated release of AA by phospholipases in the skin
result in increased PGs levels. PGE
2
resulting from in-
creased COX-2 expression contributes to the uncontrolled
proliferation of damaged cells that ultimately form tumors
in the skin. COX-2 overexpression and elevated PGE
2
lev-
els have been demonstrated in both pre-malignant skin le-
sions and skin cancers, as well as skin cancer cell lines. In
addition, levels of COX-2 activity seem to increase with an
invasive potential and seriousness of skin tumors. Normal
skin has very low levels of COX-2 and PGE
2
, pre-malig-
nant human actinic keratosis lesions have increased levels
of COX-2 and PGE
2
, and SCCs have the highest levels of
COX-2 and PGE
2
(ref.
7
). PGE
2
interacts with the cytokine
cascade including IL-4 and IL-10, which are responsible
for the UV-induced systemic immune suppression
3
.
Heme oxygenase
Heme oxygenase (HO; EC 1.14.99.3) is a redox-regu-
lated enzyme catalyzing the degradation of heme. Two
isoforms of HO have been found in the skin, constitutive
HO-2 and inducible HO-1, which respond to a variety of
oxidative stressors, including UVA radiation and H
2
O
2
(ref.
35
). UVB has been reported to be only weak HO-1
inducer
36
. Both non-enzymatic as well as enzymatic LPx
of internal membrane lipids, a decrease in the intracellular
GSH levels and the integrity of the cytoplasmatic mem-
brane are all important for the UVA-mediated induction
of HO-1 (ref.
37
). Free heme, released from microsomal
heme-containing proteins, that is generated in UVA irradi-
ated cells, also appears to be a critical intermediate that
can directly influence both the transcriptional activation
and repression of the HO-1 gene
38
. A high degree of corre-
lation was demonstrated between the amount of released
heme and the degree of a subsequent induction of HO-1
transcription following UVA and H
2
O
2
treatment
39
.
Nitric oxide synthase
Nitric oxide synthase (NOS; EC 1.14.13.39), which
produces NO from L-arginine, has two isoforms: constitu-
tive calcium-dependent (cNOS) and inducible calcium-in-
dependent (iNOS) (ref.
40
). In UVB-exposed keratinocytes
an increased expression of iNOS and a large induction of
NO were demonstrated. Higher levels of NOS activity,
stimulated by UV radiation, initiate other more complex
reactions that include various cell types. The NO liberated
following UV radiation plays a significant role in initiating
melanogenesis, erythema, and immunosuppression
41, 42
.
Ornithine decarboxylase
Ornithine decarboxylase (ODC; EC 4.1.1.17), the
first enzyme in the mammalian polyamine-biosynthesis
pathway, plays an important role in the regulation of cell
UVA (ref) UVB (ref)
MMP-1 ↑ (17, 27, 31) ↑ (27, 31)
MMP-2 ↑ (17, 27, 31) *
MMP-3 ↑ (17, 27, 31) ↑ (27, 31)
MMP-9 ↑ (17, 27) ↑ (33)
COX-2 ↑ (17, 35) ↑ (35)
HO-1 ↑ (17, 36) n (37)
iNOS * ↑ (42)
ODC * ↑ (44, 45)
p53 ↑ (17, 22) ↑ (22)
Bcl2 ↑ (17) ↑ (21)
Bax ↓ (17) ↓ (21)
c-jun ↑ (17) ↑ (7, 53)
c-fos ↑ (17) ↑ (7, 53)
AP-1 ↑ (17) ↑ (29)
NFκB ↑ (17, 52) ↑ (29, 51, 52)
TNF-α ↑ (17) ↑ (29)
IL-1 ↑ (17) ↑ (29)
IL-6 ↑ (17) ↑ (29)
Table 2. Comparison of genes products induced by
UVA and UVB radiation.
↑ - induction; ↓ - downregulation; n - no effect on this
parameter; * information was not found, probably no ef-
fect on this parameter.
32 A. Svobodova, D. Walterova, J. Vostalova
proliferation and is a well-established marker for tumor
promotion. Acute and chronic UVB exposure leads to
induction of epidermal activities and protein expres-
sion of ODC (ref.
43, 44
). UVA irradiation was not found
to significantly enhance ODC activity in human skin
fibroblasts
45
.
Cytochromes P450
Cytochromes P450 (CYP) belong to a superfamily
of microsomal membrane-bound mono-oxygenases, and
are responsible for the metabolic activation of both xe-
nobiotics and endobiotics. They also play an important
part in the protective role of the skin. The expression
of CYP genes in target cells seems to be an important
determinant in the human susceptibility to cancers in-
cluding skin cancers
46, 47
. CYP1A1, widely expressed in
extrahepatic tissues, is up-regulated in response to UV.
There is evidence that its products participate in defence
against oxidative stress. In skin, molecular epidemio-
logical studies have assessed CYP1A1 genotypes in BBC
(ref.
48
). UVA treatment of cultured keratinocytes induced
CYP4A11 mRNA expression. Therefore it may participate
in the defence mechanism against UVA-induced oxida-
tive damage
47
. It has also been demonstrated that UVB
induced both CYP1A1 and CYP1B1 gene expression in
human skin. This will probably result in enhanced bioac-
tivation of polycyclic aromatic hydrocarbons and other
environmental pollutants to which humans are exposed,
which in turn could make the human skin more suscep-
tible to ultraviolet-B-induced skin cancers or allergic and
irritant contact dermatitis
46, 49
.
PREVENTION OF UV-INDUCED SKIN DAMAGE
Since the primary function of the skin is to protect
the organism against the harmful effect of the environ-
ment it has several mechanisms to prevent UV-induced
skin alteration. These include cell cycle arrest, apoptosis,
where the p53 protein plays an important role, activation
of cell survival and proliferation as well as a mechanism
to modulate ROS/RNS, including gene expression of skin
antioxidant enzymes
1, 20
.
Another possibility for cutaneous photoprotection is
exogenous application of substances to the skin that sup-
port the skin’s own protective mechanisms or attenuate
the UV penetrating to the skin.
A) ENDOGENOUS MECHANISMS
Induction of p53 protein
The p53 protein, encoded by the tumor suppressor
gene p53, is important in both growth arrest and apop-
tosis. Upon DNA damage by acute UV radiation, p53
transcription is up-regulated, and p53 protein is activated
by phosphorylation at multiple serine residues, includ-
ing Ser 15, Ser 20, Ser 33, Ser 37, Ser 46, and Ser 392.
Various protein kinases such as ATM (ataxia-telangiecta-
sia-mutated) and ATR (ATM-related), p38, and MAPKs
are involved in the phosphorylation of various p53 serine
residues in response to UV radiation
1, 20
. UVA exposure
leads to less pronounced and more short-lived p53 activa-
tion in comparison to UVB
21
.
The repair of photo-lesions is the primary response
to DNA photodamage in surviving cells. However, if the
damage persists into the S phase of the cell cycle, other re-
pair mechanisms can lead to mutagenesis resulting mainly
in a characteristic cytosine to thymine substitution. When
such mutations occur in the p53 gene, cells lose their abil-
ity to undergo the apoptotic process
3,7
.
Cell cycle arrest
Cell cycle regulation plays an important role in main-
taining the genetic integrity of the cell. A prolonged G1
phase of the cell cycle due to the accumulation of the
activated p53 protein is a characteristic of UVB damaged
cells. This allows cells enough time to repair DNA dam-
age before its replication in the S phase or it induces ap-
optosis in cells with extensive DNA damage. Enhanced
expression of cell cycle regulatory proteins such as CDKs
and cyclins, and/or decreased or lost expression of cy-
clin-dependent kinases inhibitors (CDKIs) are causally
observed after UV radiation. The G1 cell cycle arrest is
usually accompanied by an increase in CDKI, Cip1/p21
protein, the universal inhibitor of cell cycle progression,
in p53-dependent or -independent manner
1, 20
.
Activation of apoptosis
If the DNA damage caused by UV radiation is very
severe and cannot be repaired, apoptotic pathways are
activated to eliminate damaged cells. Protein p53 as a
transactivator of transcription can induce apoptosis by
up-regulating the expression of pro-apoptotic genes such
as Bax and Fas. Protein p53 mediates cytoplasmic redis-
tribution of death receptor Fas to the cell surface. The
Fas-Fas ligand interaction results in the cleavage of pro-
caspase-8 and release of cytochrome c from mitochondria.
The subsequent reaction of cytochrome c with the apop-
tosis protease-activating factor-1 protein, a key regulator
of the mitochondrial apoptotic pathway, results in the
recruitment of procaspase-9, activation of the apopto-
somal complex, the processing of caspase-3, and finally
in apoptosis
1, 20
.
Protein p53 also down-regulates the expression of anti-
apoptotic genes such as Bcl-2 (ref.
20
). Findings in mice
suggest that apoptosis in response to UV radiation is me-
diated, at least in part, by the p53/p21/Bax/Bcl-2 pathway
and the dead cells may be replaced by hyperproliferative
cells, leading to epidermal hyperplasia. This implies that
UV-induced apoptosis and hyperplasia are closely linked,
tightly regulated and that deregulation of these pathways
may lead to skin cancer development
1
.
Activation of cell survival and proliferation
At the same time as UV activates cell-cycle check-points
and apoptosis, it also stimulates cell surviving mechanisms
and induces cell proliferation. UV radiation triggers these
33 Ultraviolet light induced alteration to the skin
processes by activating receptors or inhibitors of various
growth factors and cytokines. Recent studies have demon-
strated that the superfamily of proline/threonine MAPKs,
NFκB and AP-1 play essential roles in mediating the bio-
logical effects of UV radiation
1, 13
.

MAPKs are divided into
the extracellular signal-regulated kinases (ERKs), which
include p44 (ERK1), and p42 (ERK2), and the stress-acti-
vated protein kinases (SAPKs), which are further divided
into the c-Jun N-terminal kinases (JNKs; SAPK1), and
the p38 kinases (SAPK2). The mechanisms mediating
MAPKs activation by UV radiation are multifactorial
1,7
.
Proliferating human epidermal keratinocytes respond to
UVB in a unique manner in that prior to ERK1/2 activa-
tion, UVB causes a transient but potent down-regulation
of the Ras-ERK1/2 signalling cascade
1
.
NFκB is ubiquitously expressed in an inactive form
in most cells, composed

of NFκB p50 and Rel A p65
subunits, and bound to an inhibitory

protein, Iota kappa
B alpha (ΙκBα). In response to various stimuli, including
UVA/UVB light, inflammatory cytokines, DNA damage
and variety of mitogens, cytokine is activated and regu-
lates genes involved in inflammation, immunity, cell cy-
cle progression, apoptosis, and oncogenesis
7, 50, 51
. NF-κB
activation contributes to the production of interleukins
or TNF-α and seems to be subject to redox regulation,
suggesting thus an important role of antioxidants in its
inactivation. The precise mechanism of NFκB activation
by UV radiation is still unclear, but evidence suggests the
involvement of ROS, inhibition of the Iota kappa B alpha
(ΙκBα) (a negative regulator of NFκB), and the induction
of TNF-α receptor 1/TNF-α receptor-associated factor-2
signaling
1
. In particular, the targeted inhibition of NFκB
in the epidermis leads to an increased number of apop-
totic keratinocytes and the spontaneous development of
SCCs.
AP-1, a member of the transcription factor proteins
family, regulates the expression and function of a number
of cell cycle regulatory proteins, such as cyclin D1, p53,
p21, p 19, and p16. AP-1 is a protein dimer consisting
of either heterodimers between fos (c-fos, fos B, Fra-1,
Fra-2) and jun (c-jun, Jun B, Jun D) family proteins or
homodimer of jun family proteins. UVB strongly induces
c-jun and c-fos in human primary keratinocytes
7
as well
as in rat skin
52
. It is suggested that c-fos expression may
play a key role in UVB induced AP-1 activation in human
keratinocytes. Proto-oncogene c-fos controls cell prolifera-
tion and differentiation. It is critical for the regulation
of the DNA replication after UV radiation. It eliminates
the UV-induced block of the replication and thus appears
to play a decisive role in the cellular defence against the
genotoxic effect of UV radiation
2
.
Skin antioxidant enzymes
Superoxide dismutase (SOD; EC 1.15.1.1) belongs to
major AOx enzymes that contribute to the homeostasis
of oxygen radicals in the epidermis and thus critically
participates in the control of senescence and tumor gen-
eration. It exists in isozymes, cytosolic CuZnSOD and mi-
tochondrial MnSOD (ref.
53
). Several studies have shown a
decrease in SOD activity after UVA/UVB exposure. Single
and repetitive low doses of UVA exposure to human der-
mal fibroblasts in vitro resulted in a significant increase
in MnSOD on both mRNA and protein levels, and this
induction afforded substantial protection against the cyto-
toxic effect of the UVA insult
6
. UVB irradiation of human
keratinocytes was demonstrated to induce a significant
increase in SOD activity and protein level. This increase
in SOD was attributed to CuZnSOD (ref.
53
). UVB irra-
diation of the epidermal keratinocytes induced release of
IL-1α, IL-1β, and TNF-α that amplified MnSOD activity
in dermal human dermal fibroblasts
54
.
Glutathione peroxidase (GPx; EC 1.11.1.9) is a seleno-
protein, that catalyses the conversion of UV-induced H
2
O
2

into water and molecular oxygen using GSH as a cosub-
strate. The activity is not strongly affected by UV and is
considered to be the most important AOx defence system
in the skin
6
Catalase (CAT; EC 1.11.1.6) catalyses the conversion
of H
2
O
2
into water and molecular oxygen thus reduces
the damaging effects of H
2
O
2
. CAT activity in the skin
is strongly reduced after UVA and UVB exposure. This
decrease is probably due to irreversible oxidation of the
enzyme
6
.
B) EXOGENOUS PHOTOPROTECTION
Public health authorities recommend a variety ways to
limit sun exposure to avoid UV radiation induced injury,
such as a use of sunscreens, wearing protective clothing,
hats and sunglasses, limiting time spent outdoors during
the hours of the highest sun’s intensity (10:00 a.m. – 4:00
p.m. or at least 11:00 a.m. – 1:00 p.m.), and use of shade.
Of these, the sunscreen use is advised as a primary preven-
tion strategy against sunlight damage
55
. Despite extensive
use of sunscreens during last two decades, the incidence
of skin cancer has been increasing. The protective activity
of sunscreens/their active ingredients is largely based on
animal experiments, as it is difficult to carry out long-term
studies on humans. Hence lately the role of sunscreens in
protecting against skin cancer is intensively discussed.
In a limited number of studies, sunscreen application
was demonstrated to decrease the formation of actinic
keratoses, which are connected with SCCs. In animal
models sunscreens were shown to reduce the incidence
of BCCs and SCCs, which are linked to UVB irradiation
56
.
However, in several (9 of 15) epidemiological studies, the
use of sunscreens was associated with increased melanoma
risk
57
. The efficacy of sunscreens is traditionally assessed
using the sun protection factor (SPF). This is defined as
the ratio of the least amount of UV energy required to pro-
duce minimal erythema on the sunscreen protected skin
to the amount of energy required to produce the same
erythema on the unprotected skin
58
. Thus SPF is based
solely on a prevention of erythema (sunburn), which is
primarily caused by UVB. Thus it cannot be used as an
indicator of the damage induced by UVA irradiation. Thus
users of the high factor sunscreens may have an artificial
34 A. Svobodova, D. Walterova, J. Vostalova
sense of security that they are similarly protected against
UVA which leads to prolonged sunbathing. So the use of
high factor sunscreens may paradoxically be associated
with the increased skin cancer risk. Several methods for
evaluation of the skin UVA-photoprotection afforded by
sunscreens exist, however these methods have not been
validated and none is universally accepted
56
. The most
frequently used in vivo method is the persistent pigment
darkening (PPD), in which irradiation of volunteers with
a pure UVA light source induces pigmentation
59
.
Moreover the SPF is assessed after phototesting in vivo
at an internationally agreed application dose of 2.0 mg.
cm
–2
. However, a number of studies have shown that con-
sumers apply much less than this, typically between 0.5
– 1.5 mg.cm
–2
(ref.
58
). The dose of applied sunscreen is
critical for the degree of photoprotection (see Tab. 3)
(ref.
60
).
Through the 20
th
century, numerous UV filters having
unique characteristic were introduced. These included
mainly aminobenzoates, benzophenones, cinnamates,
salicylates, camphor derivatives and metal oxides
61
. In
European Union (Directive EEC 76/768; 1999; Tab. 4)
28 substances are allowed for sun protective cosmetic. In
the Czech Republic (Executive orders No. 174/1998; No.
444/2004; 126/2005; Tab. 4), 23 UV-filters are permitted.
In USA (US Food and Drug Administration Sunscreen
Monograph Final Rule, 1999; Tab. 4) it is only 16 com-
pounds, which are considered as drugs (camphor de-
rivatives are not allowed)
62
. However, several substances
widely used in sunscreens were found to be questinable.
For example Parsol 1789, a widely used UVA-absorbing
agent present in sunscreens, has been recently found to
inadequately protect human keratinocytes from UVA
damage
63
. Esters of p-aminobenzoic acid were recognized
to be phototoxic
57
. Benzophenone-3 was demonstrated
to be a photoallergen
60
. Currently used sunscreens do
not completely prevent photoaging, photo-immunosup-
pression or photocarcinogenesis. Inadequate protection
of sunscreens may be associated with the lack durability
of the application, the lack or inadequacy of UVA filters
in sunscreens, the photo-instability of sunscreens filters/
components which result in less protection
56
. Thus there
is the need to find efficient UVA photoprotectives and to
develop the broad-spectrum sunscreens.
As ROS were established to be responsible for UVA-
induced carcinogenesis one strategy for UVA-photopro-
tection is the support of the endogenous antioxidant
system. One alternative to suppressing UV radiation-in-
duced ROS/RNS-mediated injury is the use of compounds
naturally present in the skin especially vitamins. However,
the effectiveness of vitamin C, E and A (or β-carotene)
in photoprotection is still discussed due to their form of
use. While free, but unstable forms are effective, their
more stable derivatives (esters) are not powerful in UV
protection
26,64
. Thus various natural substances and plant
extracts have been studied. Among these, the phenolics
have gained prominent importance.
As mentioned above UVB was for a long time con-
sidered to be responsible for the UV-induced deleterious
effect and for this reason most studies were done on the
UVB region. UVB protoprotectivity was shown in several
polyphenols and plant extracts such as caffeic and feru-
lic acid, resveratrol, apigenin, genistein, quercetin
5
, green
tea and its components epikatechin and epigalokatechin-
3-gallate
65, 66
, silymarin (a standardized extract from the
seeds of Silybum marianum) and its main component
silybin
67, 68
, Pinus pinaster bark extract, Ginkgo biloba leaves
extract
65,
Polypodium leucotomos extract
69
or Prunella vul-
garis extract
70
. Intense investigation of UV influence on
the skin revealed that the UVA part is also involved in
induction and development of skin cancer. To date only
few substances/extracts have been demonstrated to be ca-
pable of protecting/suppressing UVA-induced skin cells/
skin injury e.g. carnosic acid
71
, quercetin
72
, epikatechin
74
,
epigallokatechin-3-gallate
74, 75
or P. leucotomos extract
76
,
silymarin
77
and P. vulgaris extract
78
. Considering the lat-
est knowledge about UV radiation it is necessary to look
for new substances possessing both UVA and UVB pro-
tection.
CONCLUSION
It is well known that UV radiation present in sunlight
is a potent human carcinogen. It induces various acute and
chronic reactions in human and animal skin. Fortunately,
cells are equipped with a variety of mechanisms that
constantly monitor and repair most of the UV-induced
damage. The nucleotide excision repair system prevents
the DNA damage from leading to DNA mutations and
finally, to skin carcinogenesis. In this process, the p53
gene plays a crucial role by causing cell cycle arrest, giv-
ing cell time for DNA repair, or inducing the cell death
by apoptosis when the DNA damage cannot be repaired.
Other mechanisms such as enzymatic and non-enzymatic
antioxidants help cells to eliminate reactive oxygen and
nitrogen species, which are extensively generated after UV
exposure. Therefore the development of effective strate-
gies to support cellular protection mechanisms appears
to be promising in the prevention and therapy of human
cutaneous carcinogenesis.
0.5 1.5 1.5 2
Declared SPF
2 1.2 1.4 1.7 2.0
4 1.4 2.0 2.8 4.0
8 1.7 2.8 4.8 8.0
15 2.0 3.9 7.6 15.0
30 2.3 5.5 12.8 30.0
50 2.7 7.1 18.8 50
Dose of sunscreen (mg/cm
2
)
Real-valued SPF
Table 3. Relationship between the sun protection factor
(SPF) and applied sunscreen dose (taken from ref
26
).
35 Ultraviolet light induced alteration to the skin
Table 4. List of permitted UV filters in cosmetic product (Part A).
No. SUBSTANCE(S)
Chemical name (INCI Names/synonyms ) Major trade names
1 4-Aminobenzoic acid (PABA)
a b c
2 N,N,N-Trimethyl-4-(2-oxoborn-3-ylidenmethyl) anilinium methylsulphate
(Camphor benzalkonium methosulfate)
Meroxyl SO
a b
3 3,3,5-Trimethylcyclohexyl-salicylate ((3,3,5-trimethylcyclohexyl) 2-
hydroxybenzoate (Homosalate)
Eusolex HMS
a b c
4 2-Hydroxy-4-methoxybenzophenone (Benzophenone-3; Oxybenzone ) Uvinul D50
Eusolex 4360
Neo Heliopan B
a b c
5 2-Cyano-3,3-diphenyl acrylic acid, 2-ethylhexyl ester (Octocrylene) Uvinul N539
Parsol 340
Eusolex ORC
Neo Heliopan 303
a b c
6 2-Phenylbenzimidazole-5-sulphonic acid (Phenylbenzimidazole sulfonic
acid; Ensulizole ) and its potassium, sodium and triethanloamine salts
Eusolex 232
Neo Heliopan HS
a b c
7 Ethoxylated ethyl-4-aminobenzoate (PEG-25 PABA) Uvinul P25
a b
8 2-Ethylhexyl salicylate (Octyl salicylate; Octisalate ) Eusolex OS
Neo Heliopan OS
Solarom OS
a b c
9 2-Ethylhexyl-4-methoxycinnamate (Octyl methoxycinnamate; Octinoxate ) Parsol MCX
Uvinul MC 80
Solarom OCM
a b c
10 Isopentyl-4-methoxycinnamate (Isoamyl p-methoxycinnamate; Isopentyl p-
methoxycinnamate )
Neo Heliopan E-1000
a b
11 1-(4-tert-Butylphenyl)-3-(4-methoxyphenyl) propane-1,3-dione (Butyl
methoxydibenzoyl methane; Avobenzone )
Parsol 1789
Eusolex 9820
Neo Heliopan 357
a b c
12 3,3´-(1,4-Phenylenedimethylene) bis(7,7-dimethyl-2-oxo-bicyclo-
[2,2,1]hept-1-yl-methanesulphonic acid and its salts (Terephthalylidene
dicamphor sulfonic acid; Ecamsule )
Meroxyl SX
a b
13 4-Dimethyl-aminobenzoate of ethyl-2-hexyl (Octyl dimethyl PABA; Octyl
dimethyl-4-aminobenzoate ; Padimate O)
Eusolex 6007
Uvasorb DMO
a b c
14 2-Hydroxy-4-methoxybenzophenone-5-sulphonic acid (Benzophenone-4 ;
Sulisobenzone) and its sodium salt (Benzophenone-5 ; Sulisobenzone
sodium)
Uvinul MS40
a b c
15 alpha-(2-Oxoborn-3-ylidene)-toluene-4-sulphonic acid and its salts
(Benzylidene camphor sulfonic acid and salts)
Meroxyl SL
a b
16 3-(4´-Methylbenzylidene-d-1-camphor) (4-methylbenzylidene camphor;
Enzacamene )
Eusolex 6300
Parsol 5000
Neo Heliopan MBC
a b
17 3-Benzylidene camphor Meroxyl SDS-20
a b
18 (4-(1-methylethyl)pentyl)methyl salicilate (Isopropylbenzyl-salicylate;
Megasol )
a
19 2,4,6-Trianilin-(p-carbo-2´-ethylhexyl-1´-oxy)-1,3,5-triazine (Octyl
triazone; Ethylhexyl Triazone )
Uvinul T 150
a b
a
in the Czech Republic (Executive orders No. 174/1998, No. 444/2004, 126/2005);
b
in European Union (Directive
EEC 76/768);
c
in USA (Food and Drug Administration Sunscreen Monograph Final Rule).
36 A. Svobodova, D. Walterova, J. Vostalova
Table 4. List of permitted UV filters in cosmetic product (Part B).
No. SUBSTANCE(S)
Chemical name (INCI Names/synonyms ) Major trade names
20 Polymer of N-{(2 and 4)-[(2-oxoborn-3-ylidene)methyl]benzyl}acrylamide
(Polyacrylamidomethyl benzilidene camphor)
Meroxyl SW
a b
21 (1,3,5)-Triazine-2.4-bis((4-(2-ethylhexyloxy)-2-hydroxy)phenyl)-6-(4-
methoxyphenyl) (Anisotriazine)
Tinosorb S
b
22 2,2´-Methylene-bis-6-(benzotriazol-2yl)-4-(tetramethyl-butyl)-1,1,3,3,-
phenol (Methylene bisbenzotriazolyl tetramethyl butyl phenol)
Tinosorb M
b
23 Benzoic acid, 4,4-((6-(((1,1-
dimethylethyl)amino)carbonyl)phenyl)amino)1,3,5-triazine-
2,4diyl)diimino)bis-,bis-(2-ethylhexyl)ester) (Dioctyl butamido triazone;
Diethylhexyl Butamido Triazone )
Uvasorb HEB
b
24 Monosodium salt of 2,2´-bis-(1,4phenylene)1H-benzimidazole-4,6-
disulphonic acid) (Bisymidazylate)
b
25 Phenol, 2-(2H-benzotriazol-2-yl)-4-methyl-6-(2-methyl-3-(1,3,3,3-
tetramethyl-1-(trimethylsilyl)oxy)disiloxanyl)propyl) or 2-(2 H-
benzotriazolyl)6{[3(1,1,1,3,5,5, 5-heptamethyltrisiloxan-3-yl]2-
methylpropyl}4-methylfenol (Drometrizole trisiloxane)
Meroxyl XL
Sialtrizole
b
26 Dimethicodiethylbenzal malonate (Polysilicone-15) Parsol SLX
a b
27 2-(4-(Diethylamino)-2-hydroxybenzoyl-hexylbenzoate (Diethylamino
hydroxybenzoyl hexyl benzoate)
Uvinul A Plus
a b
28 Dioxybenzone (Benzophenone-8) Spectra Sorb UV-24
c
29 Trolamine salicylate Neo Heliopan TES
Sunarom TS
c
30 Menthyl anthranilate (Meradimate) Neo Heliopan MA
Solarom MA
c
31 2-Ethoxyethyl p-methoxycinnamate (Cinoxate)
c
32 Titanium dioxie; micronized Hombitec L7
a b c
33 Zinc oxide; micronized Zinkoxid
b c
a
in the Czech Republic (Executive orders No. 174/1998, No. 444/2004, 126/2005);
b
in European Union (Directive
EEC 76/768);
c
in USA (Food and Drug Administration Sunscreen Monograph Final Rule).
ACKNOWLEDGEMENT
This work was supported by the Ministry of Education of
the Czech Republic (Research concept MSM 6198959216).
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