Sunscreens (Monograph)

Drug class: Sunscreen Agents
ATC class: C01DA02
VA class: DE350
CAS number: 150-13-0

Medically reviewed by Drugs.com on Dec 23, 2024. Written by ASHP.

Introduction

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

Uses for 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.

Sunscreens Dosage and Administration

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.

Cautions for Sunscreens

Little information is available regarding the safety of chronic sunscreen usage, but commercially available physical and chemical sunscreens appear to have a low incidence of adverse effects. Derivatives of PABA, benzophenone, cinnamic acid, and salicylate and 2-phenylbenzimidazole-5-sulfonic acid have caused skin irritation including burning, stinging, pruritus, and erythema on rare occasions. Skin irritation produced by padimate A appears to be dose related.

PABA derivatives reportedly have weak sensitization potential, but the incidence of allergic and photoallergic contact dermatitis associated with their use is increasing. Contamination of PABA derivatives with benzocaine which may cause allergic reactions has been reported. In patients allergic to compounds that are structurally similar to PABA (e.g., ester-type anesthetics, aniline dyes, thiazides, sulfonylurea and paraphenylenediamine drugs), cross-sensitivity to PABA derivatives has been reported occasionally; therefore, sunscreens containing PABA derivatives may be contraindicated in patients with a history of hypersensitivity to these chemicals.

If skin irritation or a rash occurs during use of a sunscreen product, use of the sunscreen should be discontinued and the sunscreen washed off. If irritation persists, a physician should be consulted. Contact of sunscreen agents with the eyes should be avoided. If the sunscreen comes in contact with the eyes, the affected eye(s) should be flushed thoroughly with water.

The manufacturers of sunscreen preparations with propellants warn that concentrating and subsequently inhaling the fumes from these preparations may be harmful or fatal.

Because the absorptive characteristics of skin of children younger than 6 months of age may differ from those of adults and because the immaturity of metabolic and excretory pathways of these children may limit their ability to eliminate any percutaneously absorbed sunscreen agent, sunscreen products should be used in children younger than 6 months of age only as directed by a clinician. It is possible that the characteristics of geriatric skin also differ from those of skin in younger adults, but these characteristics and the need for special considerations regarding use of sunscreen preparations in this age group are poorly understood.

PABA and, to a much lesser extent, PABA esters may permanently stain light-colored clothing and upholstery yellow or brown. Clothing should not be put over the treated area until the applied product has dried.

Manufacturers of suntanning products that do not contain sunscreen ingredients (e.g., moisturizers used during tanning, products that give the appearance of a tan by imparting color to the skin) should warn that such products do not protect the skin from sunburn. Repeated exposure of unprotected skin while tanning may increase the risk of skin aging, skin cancer, and other harmful effects to the skin even if sunburn does not occur.

Pharmacology

Radiation from the sun that reaches the earth’s surface is composed of infrared light (wavelengths greater than 760 nm), visible light (wavelengths of 400–760 nm), and ultraviolet (UV) radiation with wavelengths of 100–400 nm (principally 290–400 nm). UV radiation wavelengths of 290–320 nm (UVB) produce sunburn and tanning, and those of 320–400 nm (UVA) produce only tanning.

Opaque, physical sunscreens reflect and scatter all radiation in the UV and visible range, thereby preventing or minimizing burning and tanning.

Radiation is absorbed by chemical sunscreens when the electron energy level of the drug is raised from its ground state to a higher energy level or excited state. Chromophore groups (C=C, C=O, O—N=O) with loosely held electrons are easily excited by radiation. Compounds which have several chromophore groups in optimal positions have high absorbance over a broad range of wavelengths.

Chemical sunscreens are usually agents that absorb not less than 85% of UVB radiation (thus preventing burning) but may permit transmission of UVA radiation (thus allowing tanning). Some sunscreens may absorb wavelengths over a range that is slightly wider or narrower than that of UVB. All PABA derivatives absorb wavelengths of approximately 290–320 nm, benzophenone derivatives absorb wavelengths of approximately 250–360 nm, cinnamic acid derivatives absorb wavelengths of 280–320 nm, and salicylate derivatives and other miscellaneous chemical sunscreens absorb wavelengths of about 270–320 nm.

The wavelength to which the skin is maximally sensitive had been accepted for many years to be 296.7 nm; however, recent evidence suggests that the most erythemogenic UVB wavelength may be slightly lower (e.g., somewhere in the range of 292–295 nm). In addition, of the stronger burning wavelengths that reach the earth’s surface, most are approximately 310 nm. Therefore, sunscreens that maximally absorb UVB radiation near either of these wavelengths are particularly effective at preventing sunburn. Maximum absorbance occurs at about 290 nm for PABA, at about 295 nm for glyceryl-p-aminobenzoate, and at about 310 nm for the remaining PABA derivatives. Maximum absorbance occurs at 280–290 nm for benzophenone derivatives, at 310 nm for cinnamic acid derivatives with the exception of diethanolamine-p-methoxycinnamate which has its maximum absorbance at 290 nm, and at 300–305 nm for salicylate derivatives and other miscellaneous sunscreens.

Sunscreen effectiveness also depends on the amount of radiant energy that a sunscreen is able to absorb (molar absorptivity); as the molar absorptivity increases, less UVB radiant energy reaches the skin. Molar absorptivity is directly proportional to the concentration and residual thickness of a sunscreen applied to the skin. Products having high molar absorptivities and sunscreen concentrations are more effective than those having low absorptivities and sunscreen concentrations. However, the effectiveness of a sunscreen product having a low or intermediate molar absorptivity can be enhanced by increasing the concentration of the sunscreen or by adding additional sunscreen agents. Similarly, maximum absorbance is sometimes improved by changing the pH or the solvent of a sunscreen product.

The sunscreen protection factor (SPF) is essentially a factor that accounts for all the variables (UV absorption range, maximum absorbance, molar absorptivity, concentration, pH, solvent) that determine the effectiveness of a sunscreen product. SPFs are derived by dividing the minimum dose of sunlight needed to produce erythema (MED) on sunscreen-protected skin by that dose producing the same effect on unprotected skin. The US Food and Drug Administration’s (FDA) approved method for determining SPFs relies on a solar simulator. Sunlight generally cannot be used because it is too variable. However, some clinicians believe that use of a solar simulator on a small number of test subjects may not provide an accurate indication of a product’s effectiveness. Sunscreens with SPFs of 2 to less than 4 afford only minimum protection against sunburn but permit suntanning; SPFs of 4 to less than 8 allow moderate sunburn protection and UVB exposures of 4–8 times longer than unprotected skin but permit some suntanning; SPFs of 8 to less than 12 provide high sunburn protection and allow UVB exposures of 8–12 times longer than unprotected skin and permit limited suntanning; SPFs of 12 to less than 20 provide very high sunburn protection and UVB exposures of 12–20 times longer than unprotected skin and permit little or no suntanning; and SPFs of 20-30 provide ultra high sunburn protection, offering the most protection and permitting no suntanning.

Effective May 21, 2001, the FDA is condensing these categories into 3 broader groups of sunscreen products and has generalized the category designations. Sunscreens with SPFs of 2 to less than 12 afford minimal protection against sunburn and tanning; SPFs of 12 to less than 30 allow moderate sunburn or suntan protection; and SPFs of 30 and above provide high protection against sunburn or tanning.

Although sunscreens claiming specific SPFs greater than 30 currently are commercially available, FDA states that the additional protective benefit provided by preparations with such claimed SPFs is negligible. In fact, the additional protection provided by sunscreens with an SPF of 40 or 50 is so small as to be clinically inapparent, particularly considering the biologic interindividual variability in response to the protective quality of sunscreens. Effective May 21, 2001, the FDA will no longer permit SPFs exceeding 30 on sunscreen labels; instead, the agency has ruled that such products may be labeled SPF 30+ (or 30 plus).

Sunscreens Pharmacokinetics

Information on the cutaneous absorption, distribution, and elimination of most topically applied sunscreen agents is limited. Solvents used in sunscreen products affect the stability and binding of the drug to the skin; in general, alcoholic solvents allow for the most rapid and deepest epidermal penetration of sunscreens. It appears that sunscreen agents are absorbed by the intact epidermis to varying degrees. PABA reportedly diffuses into the stratum corneum, reaching maximum concentrations there 2 hours following application, but apparently does not penetrate deeper layers of the skin to a substantial extent. Homosalate’s penetration also appears to be limited to the stratum corneum. One study in animals indicated that PABA may penetrate the skin to a greater extent than does padimate A. Although some studies have shown that substantive concentrations of PABA remain on the skin after washing, other studies have failed to confirm this. One study showed that PABA esters were removed from the skin less readily than was PABA or other chemical sunscreens.

Chemistry

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

Chemical Sunscreens

Aminobenzoic Acid Derivatives

Aminobenzoic acid (PABA)

The drug occurs as white or slightly yellow, odorless crystals or crystalline powder. The drug is slightly soluble in water and freely soluble in alcohol. PABA is incompatible with ferric salts and oxidizing agents and darkens on exposure to air or light; preparations of the drug should be stored in light-resistant containers.

Ethyl-4-bis-(hydroxypropyl)-1-aminobenzoate

The drug is the 2 mole propoxylate of aminoethylbenzoate and ethylhydroxypropyl PABA, is insoluble in water and soluble in alcohol.

Glyceryl-p-aminobenzoate

The drug is the glyceryl ester of PABA and occurs as a pale yellow to amber, semisolid, waxy mass or syrup having a faint aromatic odor. The drug is insoluble in water and soluble in alcohol.

Menthyl anthranilate

The drug is the menthyl ester of anthranilic acid and occurs as an amber, viscous liquid and is insoluble in water and soluble in alcohol.

Padimate A

The drug is a mixture of pentyl, isopentyl, and 2-methylbutyl p-(dimethylamino)benzoates and occurs as a yellow, faintly aromatic liquid. The drug is insoluble in water and soluble in alcohol.

Padimate O

The drug is the 2-ethylhexyl ester of p-(dimethylamino) benzoic acid, occurs as a clear to yellow, oily liquid having a faint aromatic odor and is insoluble in water and soluble in alcohol.

Benzophenone Derivatives

Dioxybenzone and Oxybenzone

The drugs occur as off-white to yellow powders and are practically insoluble in water and freely soluble in alcohol.

Cinnamic Acid Derivatives

Cinoxate

The drug occurs as a slightly yellow, practically odorless, viscous liquid and is very slightly soluble in water and miscible with alcohol.

Diethanolamine-p-methoxycinnamate

The drug occurs as a pale tan, microcrystalline powder and is freely soluble in water.

Octyl methoxycinnamate

The drug occurs as a practically odorless, pale yellow, slightly oily liquid and is insoluble in water and miscible with alcohol.

Salicylate Derivatives

Homosalate

The drug occurs as a clear, colorless to faint yellow, oily liquid and is insoluble in water and soluble in alcohol.

Octyl salicylate (2-ethylhexyl salicylate)

The drug occurs as a clear, white to slightly yellowish liquid and is insoluble in water and miscible with alcohol.

Trolamine salicylate

The drug occurs as a waxy solid and is miscible with water and with alcohol.

Miscellaneous Chemical Sunscreens

Digalloyl trioleate

The drug is the triester of tannic and oleic acids, occurs as a clear, viscous, brown oil having a slight odor, and is insoluble in water and soluble in alcohol.

Octocrylene (2-Ethylhexyl-2-cyano-3,3-diphenylacrylate)

The drug occurs as a nonstaining, pale yellow liquid and is insoluble in water and miscible with alcohol.

2-Phenylbenzimidazole-5-sulfonic acid

The drug occurs as a white, almost odorless, finely crystalline powder and is soluble in water and in alcohol.

Opaque Physical Sunscreens

Red petrolatum

The drug is a petrolatum containing an intrinsic red pigment and is obtained from crude petroleum and a paraffin wax.

Titanium dioxide

The drug occurs as a white, odorless, tasteless powder and is insoluble in water and in alcohol.

Zinc oxide

The drug occurs as a very fine, odorless, amorphous, white or yellowish-white powder that is free from gritty particles and gradually absorbs carbon dioxide upon exposure to air. Zinc oxide is insoluble in water and in alcohol. Prolonged storage of zinc oxide preparations at temperatures greater than 30°C should be avoided.

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

Frequently asked questions

Can I apply DEET and a sunscreen at the same time?