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April 2011 Supplement to Skin & Aging 3
Sun Care
Sunscreens are essential for preventing and managing
many dermatological conditions. Although originally
developed more than 70 years ago to prevent sunburns,
sunscreens are now also used to prevent skin cancer,
photoaging,
pigmentary disorders and a myriad of other dermatoses
exacer-
bated by ultraviolet (UV) exposure.
UV Radiation: Characteristics, and Acute and
Long-Term Effects
UV Radiation Characteristics
The solar wavelengths include UV radiation, visible light
and infra red light. UV radiation can be categorized into
UVA,
UVB and UVC radiation. UVC does not reach the Earths sur-
face, so UVA and UVB are the ultraviolet rays that play a
role
in skin disease and are clinically significant. UVA
comprises
96.5% of UV radiation, and UVB comprises 3.5%.1 While
UVA makes up the vast majority of UV radiation in everyday
exposure, UVB is also important as it is considered a major
cause of DNA damage in the skin. Table 1 summarizes key
characterist ics of the solar wavelengths.
Acute Effects of UV Radiation
UV light a ffects skin immediately and long-term. The im-
mediate effects include direct DNA damage, immunosup-
pression and sunburn. Cyclobutane pyrimidine dimers are
the most common type of DNA damage in the skin after
UV exposu re; however, the effects of UV rad iation on DNA
is actually more complex. After UV exposure, p53 muta-
tions and pyrimidine-pyrimidone 6-4 photoproducts are
observed. In addition, oxidative stress and an inf lammatory
response are noted.2 4
Human skin has complex repair mechanisms to combat acute
UV-induced DNA damage via photolyase, nucleotide excision
repair enzymes and an antioxidant network.5 Melanin
synthesis
after UV exposure is another mechanism to combat UV dam-
age. The melanin observed after UV exposure and the melanin
observed in darkly pigmented individuals is most apparent in
the
apical portion of the keratinocytes. This melanin blocks UV
and
scatters UV radiat ion to prevent damage of the DNA contents
of
the cells.6 Its not surprising that the tumor suppressor gene
p53
has recently been implicated as the gene responsible for
melano-
genesis after UV exposure.7
Immunosuppression is another immediate adverse effect of
UV radiation. Immunosuppression after UV radiation is char-
acterized by diminished antigen-presenting cell function,
induc-
tion of immunosuppressive cytokines and modulation of
contact
and delayed-type hypersensitivity reactions.8 The role of
UV-induced immunosuppression and its relation to skin cancer
has
not been fully elucidated. Systemic immunosuppression is
clearly
associated with an increased risk of skin cancer. This is
especially
evident in the renal transplant population.911 Among these
trans-
plant recipients, theres a linear increase in basal cell
carcinoma
(BCC) risk and an exponential increase in squamous cell
carci-
noma (SCC) risk.9,10
The Importance of
Photoprotection/SunscreenHeather Woolery-Lloyd, MD
Miami, FL
Table 1. Summary of Solar Wavelengths
Wavelength (nm)
Distribution of light at
the Earths surface
Ability to
penetrate glass
Level of skin
penetration
UVC 200 to 290 Stratospheric only N/A N/A
UVB 290 to 320 0.5% No Epidermis
UVA 320 to 400 9.5% Yes Dermis
Visible 400 to 800 40% Yes Hypodermis
Infrared 800 nm to 300 micrometers 50% Yes Hypodermis
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Sun Care
Sunburn, another acute effect of excessive sun exposure,
is due to UVB radiation. A sunburn is the inflammatory
process resulting from UV exposure that initiates a process
(apoptosis) that removes the irreversibly dam aged keratino-
cytes a fter excessive UV radiation. Its a mechanism of pro-
grammed cell death in severely damaged keratinocytes.12
Long-Term Effects of UV Radiation
Long-term effects of UV rad iation on the skin include the
visible signs of photoaging, epidermal thickening, skin can-
cers and pigmentary disorders. Photoaging is caused by UVA
and UVB rad iation. UVB is absorbed in the epidermis and in-
duces c-Jun; it combines with c-Fos, is natural ly abundant
and
produces activator protein-1(AP-1). Thi s transcription
factor
induces matrix metal loproteinases. In contrast to UVB, UVA
reaches the dermis and is absorbed by f ibroblasts. UVA
induc-
es reactive oxygen species. This leads to the induction of
ma-
trix metalloproteinases and mitochondrial DNA mutations.
MMP-1, known as interstitial collagenase, cleaves collagen
I, II and III. MMP-9, known as gelatinase, cleaves collagen
IV, V and gelatin. In photoaged skin, these cumulat ive
effects
result in reduction of collagens I, III and VII, increase in
elas-
totic material in the reticular dermis, and marked reduction
in
fibrillin.13 Clinically, this long-term damage to the dermis
is
characterized by fine lines, wrink ling and skin laxity.
Skin cancers are also long-term effects of chronic UV ra-
diation. Studies suggest that intense, acute exposures
result-
ing in sunburns are associated with melanoma, and chronic
UV exposure is associated with SCC.14,15 In addition, a
recent
study suggests that regular sunscreen use can prevent mela-
nomas. In this prospective study, 1621 participants were as-
signed to two groups daily suns creen to the face and arms
combined with 30 mg beta carotene, and discretionary use
of sunscreen combined with a placebo pill. The participants
participated in the study for 5 years, then were followed
for
10 years after study completion. Invasive melanoma was re-
duced 73% in the daily sunscreen group.16
Pigmentary disorders, such as solar lentigos, melasma and
post-inflammatory hyperpigmentation, are frequently ob-
served with acute and long-term UV radiation. Solar lentigosand
mottled pigmentation characteristic of photoaged skin are
due to the long-term effects of chronic sun exposure. Me-
lasma is exacerbated by acute and chronic UV r adiation.
Post-
inf lammatory hyperpigmentation can be observed with acute
UV radiation after acne, burns or any injury to the skin.
This
is especially prominent in darker skinned patients. In addi-
tion, darkly pigmented individuals often complain of
progres-
sive darkening and uneven pigmentation of facial skin with
advancing age. This progressive facial darkening is also
most
likely due to chronic UV exposure. For all disorders of
hyper-
pigmentation, and especially with melasma, sun protection is
an absolutely essential therapeutic component.
Effects of UV Radiation From Artificial Tanning Beds
Twenty-eight million Americans use artificial UV tanning
each year.17 Tanning-bed bulbs emit mostly UVA radiation and
approximately 5% UVB radiation.18 Many studies have linked
artificial tanning bed usage to melanoma.1820 Tanning bed
use
also increases the risk of non-melanoma skin cancers.21
Counsel-
ing is essential to educate patients especially teenage
patients
about the signi ficant skin cancer risks associated with arti
ficia l
tanning beds and lamps.
Photoprotection
Melanin: A Natural Photoprotectant
The photoprotection conferred by melanin in darkly pig-
mented skin greatly influences the UV-induced differences
observed in black and white skin. Epidermal architecture
in black and white subjects supports this
notion. One study demonstrated an intact,
compact stratum lucidum in sun-exposedblack skin, in contrast to
a swollen, cellular
stratum lucidum in sun-exposed white skin.
Black skin rarely exhibited atrophy, while
white skin had numerous focal areas of at-
rophy, necrosis, vacuoles and dyskeratosis.22
Melanin clearly protects against UV light.
It acts as a neutral density fi lter to equally re-
duce penetration of all wavelengths of light.23
In a study using skin samples from blacks and
whites, investigators found that five times as
much UV light reached the upper dermis of white skin when
compared to black skin. The authors determined that the main
site of UV fi ltration in white patients was the stratum
corne-
um, compared to the malpighi an layer in black patients. The
average protection offered by melanin i n black skin was
calcu-
lated to be equivalent to a sun protective factor (SPF) of
13.4
compared to 3.4 for white skin. The photoprotection observed
in black skin is due to both increased melanin content and
the
unique distribution of melanosomes in dark skin. 23
Sunscreen Agents
Various topical agents provide sun protection and prevent
the
deleterious effects of acute and chronic sun exposure.
Broad-spectrum sun protection is most desirable. For this reason,
most
In addition, darkly pigmented individuals often
complain of progressive darkening and uneven
pigmentation of facial skin with advancing age.
This progressive facial darkening is also most
likely due to chronic UV exposure.
