Chemical agents that absorb potentially harmful ultraviolet (UV) radiation or opaque, physical agents that reflect potentially harmful UV radiation are classified as sunscreens.

Sunscreen agents are used to prevent sunburn and premature aging of the skin, and to reduce the incidence of solar or actinic-induced keratoses, skin cancers, tanning, and other harmful effects of the sun. Some data suggest that carcinogenesis and photoaging can occur at doses of UV radiation below that required to produce a sunburn (i.e., suberythemal doses). Most clinicians agree that the liberal and regular use of an effective sunscreen is therapeutically desirable and not just cosmetically desirable, especially in light-skinned people with blue eyes, red hair, and/or freckles who are most susceptible to the acute and chronic harmful effects of sunlight.

Physical sunscreens effectively reflect UVB radiation but often have the disadvantage of being cosmetically unappealing. In most studies, 5% PABA in 70–90% alcohol has consistently shown superiority to other single-ingredient chemical sunscreen products. Sunscreen agents (physical or chemical) may be combined to enhance UVB absorption, but each sunscreen in the combination must contribute to the effectiveness of the product. The appropriate sunscreen product for an individual can be determined based on the patient’s skin type and the product’s SPF which is included on the label. Individuals with:

• skin type I (always burn easily, rarely tan) should use products having SPFs of 20–30 (ultra high protection)

• skin type II (always burn easily, tan minimally) should use products having SPFs of 12 to less than 20 (very high protection)

• skin type III or normal skin (burn moderately, tan gradually to a light brown) should use products having SPFs of 8 to less than 12 (high protection)

• skin type IV (burn minimally, always tan well) should use products having SPFs of 4 to less than 8 (moderate protection)

• skin type V (rarely burn, tan profusely to dark brown) should use products having SPFs of 2 to less than 4 (minimum protection)

• skin type VI (never burn, deeply pigmented) do not need a sunscreen.

However, other factors (e.g., duration of sun exposure, season, geographic location, sun reflection, history of skin cancer/precancerous changes, occupation) also influence the selection of a sunscreen product. Effective May 21, 2001, the FDA is condensing sunscreen products descriptions into 3 broad groups. Based on these changes, an alternative general guidance for product selection based on skin type and SPF has been suggested:

• those with skin that sunburns minimally may use products with SPFs of 2 to less than 12 (minimal protection)

• those with skin that sunburns easily may use products with SPFs of 12 to less than 30 (moderate protection)

• those with skin that is highly sensitive to sunburn should use products with SPFs of 30 or greater (high protection).

Even when using a sunscreen, prolonged sunlight exposure should be avoided and protective clothing should be worn by all persons, particularly those that are fair-skinned, blue-eyed, or blond. Until a protective tan develops, initial sunlight exposures should be limited to short periods, which may be gradually lengthened.

To protect against severe photosensitivity reactions of varied etiologies (e.g., erythropoietic protoporphyria, exposure to photosensitizing agents, allergic contact photodermatitis), a sequential combination of 3% dihydroxyacetone and 0.25% lawsone solutions may be used. (See Dihydroxyacetone 84:50.06.) Dihydroxyacetone or lawsone alone provides little or no UVB light protection. Although there are no comparative studies, some clinicians prefer to treat erythropoietic protoporphyria with beta carotene.

Although it has been suggested that benzophenone derivatives may protect against photosensitivity reactions to photosensitizing drugs (e.g., chlordiazepoxide, chlorpromazine, demeclocycline, hydrochlorothiazide, nalidixic acid, nystatin, sulfisoxazole), most clinicians agree that these sunscreens provide, at most, only limited protection for patients who are sensitive to these drugs.

Sunscreen agents are applied topically in the form of creams, jellies, ointments, pastes, solutions, and suspensions. Sunscreen preparations should not be administered orally. SPFs which are included in the product labeling serve as useful indices of each product’s effectiveness. (See Uses.)

Sunscreen preparations should be applied uniformly and generously to all exposed skin surfaces, including lips, before exposure to UVB radiation. Two applications of the sunscreen may be needed for maximum protection. PABA-containing sunscreens are most effective when applied 1–2 hours before exposure to sunlight. Sunscreen products that are not water resistant should be reapplied after swimming, towel-drying, or profuse sweating and, because most sunscreens are easily removed from the skin, reapplication every 1–2 hours or according to the manufacturer’s directions usually is required to provide adequate protection from UVB light.

Some sunscreens are commercially available as water-resistant or very water-resistant formulations. Following application to the skin, water-resistant sunscreen products retain their labeled SPF for prevention of sunburn after 40 minutes of activity in water (e.g., swimming) or perspiring. Very water-resistant sunscreen products retain their labeled SPF for prevention of sunburn after 80 minutes of activity in water or perspiring.