Chronic affects of sunlight include photoaging, actinic keratoses, and skin cancer. (See also Overview of Effects of Sunlight.)
Chronic exposure to sunlight ages the skin (photoaging, dermatoheliosis, extrinsic aging), primarily by causing destruction of skin collagen due to various biochemical and DNA disruptions. Skin changes include both fine and coarse wrinkles, rough leathery texture, mottled pigmentation, lentigines (large frecklelike spots), sallowness, and telangiectasia.
Actinic keratoses are precancerous changes in skin cells (keratinocytes) that are a frequent, disturbing consequence of many years of sun exposure. People with blonde or red hair, blue eyes, and skin type I or II are particularly susceptible (see Table: Fitzpatrick Skin Type Classification).
Fitzpatrick Skin Type Classification
Actinic keratoses are usually pink or red, poorly marginated, and feel rough and scaly on palpation, although some are light gray or pigmented, giving them a brown appearance.
They should be differentiated from seborrheic keratoses, which increase in number and size with age. Seborrheic keratoses tend to appear waxy and stuck-on but can take on an appearance similar to that of actinic keratoses. Close inspection usually reveals distinguishing characteristics of the lesion. Actinic keratoses can also be distinguished from a seborrheic keratosis by the rough, gritty feel of the scale and the erythema. Unlike actinic keratoses, seborrheic keratoses also occur on non–sun-exposed areas of the body and are not premalignant.
The incidence of squamous cell carcinoma and basal cell carcinoma in fair, light-skinned people is directly proportional to the total annual sunlight in the area. Such lesions are especially common among people who were extensively exposed to sunlight as children and adolescents and among those who are chronically exposed to the sun as part of their profession or recreational activities (eg, athletes, farmers, ranchers, sailors, frequent sunbathers). Sun exposure also substantially increases the risk of malignant melanoma.
Treatment begins with preventive efforts to minimize UV light exposure—avoiding the sun and tanning beds and wearing protective clothing and sunscreen.
Various combination therapies, including chemical peels, 5-fluorouracil (5-FU), topical alpha-hydroxy acids, imiquimod, photodynamic therapy, and tretinoin, have been used to reduce precancerous changes and improve the cosmetic appearance of chronically sun-damaged skin. These therapies are often effective in ameliorating superficial skin changes (eg, fine wrinkles, irregular pigmentation, sallowness, roughness, minor laxity) but have a much less pronounced effect on deeper changes (eg, telangiectasias). Many ingredients are used in over-the-counter cosmetic products without significant evidence that they improve chronic changes of the skin caused by sunlight.
There are many treatment options depending on the number of lesions, their location, and patient preference, but they are divided generally into
In lesion-targeted therapy, individual lesions are physically removed. This option may be better if the patient has only a few actinic keratoses, or if the patient is unable or unwilling to undergo other therapy options. Cryotherapy (freezing with liquid nitrogen) is the most common lesion-targeted therapy. Curettage (using electrocautery or other modality) is an alternative. Lesion-targeted therapies have the benefit of being single, in-office procedures but have a higher risk of scarring.
In field-directed therapy, topical treatments are applied to larger, more numerous, or diffuse areas of involvement. Typical agents are 5-FU (alone or in combination with calcipotriene) or imiquimod; alternatives include ingenol mebutate and topical diclofenac. These therapies cause less scarring but can be more complicated and painful for patients to use, so adherence is an issue. When large areas are involved, these therapies also cause more redness and irritation. Treatment frequency and duration vary significantly and can range from 2 times per week to 2 times per day and from 3 days to 16 weeks. Inflammation and irritation are often present during most of treatment and often for 1 to 2 weeks afterward.
Photodynamic therapy is a type of field-directed therapy. It involves topical application of a photosensitizer (eg, aminolevulinate, methyl aminolevulinate) followed by light of a specific wavelength that preferentially affects photodamaged skin. Like topical field-directed therapy, photodynamic therapy can cause redness and scaling during treatment. More than one treatment session may be needed.
For treatment of skin cancers, see Cancers of the Skin.