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Sun Damage, Actinic Damage, and Ultraviolet Carcinogenesis

Cutaneous aging results from a combination of genetically based factors and
the effects of chronic sun exposure. Senescent skin is typically thin and displays loss of
elasticity and deepened expression lines. Skin that has undergone photoaging from chronic
sun exposure, however, exhibits fine wrinkling, yellowish discoloration, laxity, a coarse 
leathery texture, telangiectasia, and mottled pigmentation. Environmental factors that may 
contribute to photoaging include wind, heat, chemical toxins, and cigarette smoke.

Studies of photoaging in such animal models as the hairless mouse have revealed that
some of the histologic damage caused by sun exposure may be reversible by avoidance of
UV light, the use of sunscreens, and topical application of tretinoin, ultraviolet, sun burn3
A 16-week randomized, double-blind study showed significant clinical improvement in
tretinoin-treated forearm skin but not in vehicle-treated skin in 30 of 40 patients.4 The greatest
change was a decrease in fine wrinkling; other documented clinical changes included an
increase in pinkness and a decrease in coarse wrinkling and

Hyperpigmentation and solar freckling became less prominent but did not disappear. There
was no apparent change in telangiectasias. Histologic changes included an increase in the
thickness of the epidermis and the granular layer and a decrease in epidermal dysplasia and
melanocyte hyperplasia. The treatment effect of decreased wrinkling could not be explained
by a retinoid-induced irritation: there was no dermal edema, and the thickness of the

The main side effects were a tretinoin-induced dermatitis consisting
of dry, erythematous, scaly patches and an increase in sun sensitivity. The formation of
collagen I was partially restored in photodamaged skin after 10 to 12 months’ application of
0.1 percent tretinoin as demonstrated by immunohistologic studies in 29 patients.5 Because
topical tretinoin has caused partial regression of actinic keratoses during treatment, it has
been suggested that this agent may have a

Normal human cells can repair DNA damage that follows UV exposure. Repair involves
recognition and enzymatic excision of the thymine dimers in altered DNA followed by de
novo synthesis of a new segment (unscheduled DNA synthesis). Under certain

The spectrum of ultraviolet radiation from the sun that induces tumors coincides with the
spectrum that causes delayed erythema. Wavelengths shorter than 280 nm (UVC, or short UV)
are absorbed by the ozone layer and do not penetrate the

Sunscreens and photoprotection Recommendations for preventing skin cancer
include minimizing direct exposure to sunlight, especially during hours of peak intensity, from

There are two main classes of sunscreens: the chemical absorbers and the physical
blockers or reflectors [see Table 1].7 The absorbers include aminobenzoic acid (PABA) and its
derivatives, which absorb mainly UVB, and the non-PABA broad-spectrum sunscreens, such

Two important properties of a sunscreen are its SPF and its substantivity, or ability to resist
removal from the skin by sweating or bathing. SPF is a measure of the effectiveness of a
sunscreen based on a comparison of the minimal erythema dose with and without the
sunscreen in a number of normal subjects. Many of the newer sunscreens with high SPF
values consist of a combination of PABA and non-PABA sunscreens.8 Sunscreens with an

Regular use of sunscreens can decrease the incidence of actinic keratoses and presumably
of their progression to skin cancer. In a randomized, controlled study from Australia, 588
patients 40 years of age or older with one to 30 actinic keratoses applied either the SPF-17
sunscreen or the placebo cream base for one summer to the head, neck, forearms, and hands.
Of the 431 patients who completed the study, those who used the sunscreen had fewer new

Ultraviolet radiation can penetrate thin, light-colored clothing, especially when the clothing
is wet. Special fabrics have been developed to provide protection for photosensitive patients
and have been reviewed under the medical-device regulations as required by the Food and
Drug Administration.10 Self-tanning lotions contain dihydroxyacetone, which is a colorless
dye that combines with free amino groups in skin protein. This cosmetic ingredient stains the


Histopathologic examination of suspected malignant lesions is essential in making a
definitive diagnosis according to established criteria.13 The type of biopsy that is performed