The effect of sunscreen on melanoma risk

History of sun protection

Because most persons experience at least one painful sunburn during their lifetime, the importance of sun protection usually has been behaviorally reinforced early in life. The importance of sun protection has also been recognized since earliest times. Ancient Egyptian art depicts persons wearing long robes and sitting in the shade of trees. Yet, it was not until the 1950s when suntan lotions came into usage. Their purpose was to help the person tan without burning. In the early 1970s, the

Sunblocks

Sunblocks physically block the sun's UV radiation to the skin. Protective clothing, umbrellas, and trees are considered sunblocks. Sunblocks can be in opaque forms and applied to the skin. When used in a topically applied form, these agents scatter, reflect, and primarily block UV light. They are partially effective for patients who have diseases related to light exposure including lupus erythematous, polymorphous light eruption, xeroderma pigmentosum, and solar urticaria. Sunblocks are also

Sunscreens

Table 1 lists common sunscreen agents and their UV protective wavelengths. PABA has been used in sunscreens in the United States since the early 1970s. One of the major characteristics of PABA that makes it effective as a sunscreen is its ability to bind to epidermal cells. This tends to make PABA-based sunscreens fairly water and perspiration resistant, but also makes them prone to staining. PABA tends to block UV radiation most effectively in the UVB zone (290 to 320 nm).

The PABA esters

Benzophenones

Benzophenones are the second most commonly found component of sunscreens. Although their primary protective range is found in the UVA range (320 to 400 nm), a secondary protective band is noted in the UVB zone. Benzophenones were originally used alone as a PABA-free sunscreen alternative, but are now combined with other sunscreen agents to provide broad-spectrum coverage.

The most commonly used benzophenone agents are oxybenzone and dioxybenzone. These ingredients are much less allergenic than

Cinnamates

Cinnamates, a derivative of cinnamon, are also good protectors from the sun. Their products are chemically related to balsam of Peru, tolu balsam, coca leaves, cinnamic aldehyde, and cinnamic oil. Persons with sensitivity to these items may cross-react to sunscreens containing cinnamates.

The most commonly used cinnamates are octyl methoxycinnamate and cinoxate. They are nonstaining but also have poor water-resistant qualities. Cinnamate products may require more frequent reapplication or

Salicylates and anthranilates

Salicylates are among the original sunscreen chemicals. Homomenthyl salicylate absorbs primarily in the UVB range and is typically added to other components to increase sun protection factor (SPF). Octyl and triethanolamine salicylates are also used. They may cause photocontact dermatitis more frequently than homomenthyl salicylate and are used less frequently.

Anthranilates, such as menthyl anthranilate, with low-level broad-spectrum coverage, are also added to many sunscreens to augment

Dibenzoylmethanes

Recent concerns over the effects of UVA radiation to the skin have demonstrated the need for better UVA protection in sunscreens. The newest ingredients that have shown to have the best UVA protection are the dibenzoylmethanes. Because they offer no protection from UVB rays, they must be used in combination with other ingredients.

Tert-butylmethoxydibenzoylmethane (Avobenzone, Parsol 1789) is approved for use in the United States. Its range of coverage is 310 to 400 nm, with a peak effectiveness

SPF System

The effectiveness of a sunscreen is measured by the use of the SPF system [5]. SPF is the ratio of the amount of time that a person exposed to the sun takes to sunburn while wearing a sunscreen compared with the time required to sunburn without protection. Initial sunscreens in the 1970s had SPFs of 2 to 4. These sunscreens, however, only provided protection from 50% to 75% of the UVB rays. Current high-potency sunscreens have SPFs ranging from 15 to 50, protecting from 93% to 98% of UVB.

Vehicles

One of the most common objections to sunscreen usage is lack of cosmetic acceptability of the product. The ingredients used to formulate sunscreen vehicles include mineral oil, petrolatum, isopropyl esters, lanolin, aliphatic alcohols, triglycerides, fatty acids, waxes, propylene glycol, emulsifiers, thickeners, preservatives, and fragrance. A sunscreen acceptable to one person or for use in a given area of the body may not be acceptable in other situations. Oil-based sunscreens may be

Protection from immunologic effects of UV radiation

A UV radiation to the skin results in various forms of local and systemic immune suppression. Release of preinflammatory cytokines (interleukin-1 and-6, tumor necrosis factor) and prostaglandins is inhibited. Langerhans' cells in the skin are depleted and inactivated. Autoimmune diseases, such as systemic lupus erythematous, can be activated. Similar activation of herpes virus eruption is noted. Allergic contact dermatitis can be suppressed. In addition, in mice, skin cancer surveillance and

Sunscreen reactions

Many types of sunscreen reactions have been reported. People often complain of a reaction to a specific sunscreen and do not subsequently use the product. These types of reactions include

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  Allergic contact dermatitis

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  Photoallergic contact dermatitis

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  Irritant dermatitis

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  Acne

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  Aesthetic issues

Because sunscreens are applied topically to the skin frequently and in relatively high concentrations (up to 26%), contact sensitization can occur. Because the active agents in sunscreens absorb radiation, they

Sunscreen protection against the development of melanoma

Whether sunscreens can reduce the risk for melanoma has not yet been proved directly [9]. Inferential evidence, however, strongly supports a protective effect. Because direct protective effects against skin cancer have only been demonstrated recently in humans [10], [11], [12] some have suggested that sunscreens might not reduce the risk for melanoma. The absence of direct proof has emboldened the most extreme critics to suggest that sunscreen use might actually increase melanoma risk [13]. It

Future trends

Many other substances are currently being investigated for their potential as sunscreens [21]. Psoralen derivatives that enhance the production of melanin are being studied. Natural substances including derivatives of coral from Australia's Great Barrier Reef have shown some early promise. Ultimately, oral preparations with appropriate concentration delivery to the skin to make the sunscreen effective will be developed.

Summary

The usage of sunscreens has grown dramatically worldwide over the past decade. Current data suggest that a regimen of sun protection that includes protective clothing, avoiding midday sun, and regular use of broad-spectrum high SPF sunscreen (such as practiced in Australia [19]) seems to be reducing melanoma incidence rates. This is the current recommendation of the American Academy of Dermatology and it is also the recommendation that is best supported by existing data.

Except for total sun