GUIDELINES FOR MINIMIZING UV EXPOSURE
Mark F. Naylor, MD
Kevin C. Farmer, PhD
Not all skins are created equal when it comes to protection from the destructive effects of UV radiation. The harmful effects of sunlight occur earlier in people with less intrinsic skin pigment, and later in people with more intrinsic skin pigment. Simply stated, the more skin pigment, the better. Because of the strong relationship between intrinsic pigmentation and natural resistance to sun damage, recommendations on sun protection should be based on estimates of intrinsic skin pigmentation.
A simple system has been devised to categorize skin pigmentation types based on previous sun exposure reactions . Those individuals having a darker constitutive (e.g., non-sun induced) pigmentation generally have a greater ability to tan. Type 1 individuals are those that never tan and always sunburn if exposed to any appreciable amount of sunlight (primarily red headed individuals and lightly complected blondes). Type 2 individuals frequently burn but are able to tan to a small degree after extended sun exposure. Type 3 individuals are those which burn infrequently and tan readily. The largest percentage of Caucasian individuals fall into pigmentation types 2 and 3. Type 4 rarely burn and tan heavily with moderate sun exposures (individuals of oriental, American Indian, Mediterranean and Latin American descent). Type 5 individuals have dark constitutive pigmentation but become noticeably darker with sun exposure (light complected black individuals, those of Indian descent). Finally, type 6 individuals are those with the heaviest constitutive pigmentation (dark skinned blacks).
Recommendations for adults can be simplified by classifying a person into one of three groups; patients requiring maximum protection, moderate protection, or minimal protection (Table 2). Table 3 contains a list of recommendations for infants and children. People that should seek maximum protection include: individuals with a previous history of skin cancer or precancerous changes, all skin type 1 individuals, individuals with skin type 2 and 3 that receive high recreational or occupational exposure, individuals with photosensitivity disorders, and finally, those desiring the maximum shielding from solar aging.
Individuals with occupational risk include obvious outdoor jobs such as agriculture workers, ranchers, roofers, postal carriers, construction workers, and forest rangers. Not so obvious outdoor occupations may include police officers, automobile salespersons, or active duty military in combat arms roles. A key question is: does the occupation require 25% or more of the working day to be spent out from under a permanent roof? Type 2 or 3 individuals that receive high recreational exposure include individuals who play golf, jog, bicycle, play tennis, or avidly pursue other outdoor sports such as skiing, or hiking.
Individuals with photosensitivity disorders that require maximum protection include people with lupus, polymorphous light eruption, melasma, or those taking potent photosensitizing medications. Drug products in which photosensitivity reactions occur fairly frequently include the topical preparations of fluorouracil, isotretinoin, coal tar containing products, and benzoyl peroxide preparations. Oral medications include psoralens, etretinate, isotretinoin, doxycycline, amiodarone, and nalidixic acid. UVA protection is of primary importance with the use of psoralens, and an avobenzone containing sunscreen (e.g., Shade® UVAGuard®) should be used with this medication.
Sunscreens may also be useful in treating or preventing photosensitiviy reactions to sulfonamides, diuretics, piroxicam, the quinolone antibiotics, and quinidine [168, 169]. Table 4 contains a list of drugs associated with photosensitivity reactions.
People requiring moderate protection include those with skin types 3 or 4 and individuals with skin types 2 or 3 with minimal occupational and recreational exposure. People that may only require minimal protection include those with skin types 2 to 4 who choose to tan (intentional tanning is not recommended), and those with skin types 5 and 6.
Individuals with skin types 1-3 (the majority of Caucasians) living in tropic and subtropic zones should develop the routine practice of using some type of sunscreen whenever they will spend time outside. Many people only think of using a sunscreen when they will be outdoors for an extended period of time during the summer months, but many of the harmful effects of sun exposure, particularly photoaging, are probably the result of cumulative time spent in the sun, including all incidental exposures.
Sunscreens should be applied liberally and uniformly to all exposed areas at least one-half hour before exposure to the skin to allow for penetration and binding to the skin. Generous and frequent product reapplication should be emphasized. Studies suggest that people often use too little of a sunscreen, and do not re-apply it frequently enough . Products containing aminobenzoic acid and its esters should be applied 1 to 2 hours before exposure.
The substantivity of a sunscreen refers to the ability of the product to adhere to the skin in the presence of sweating and swimming. Water-resistant labeled formulations will retain their photoprotective effect for up to 40 minutes of active immersion in water. Water-proof labeled formulations should retain their photoprotective effect for up to 80 minutes under similar conditions. Sweat resistant formulations retain their photoprotective effect for up to 30 minutes of continuous heavy perspiration.
The FDA has proposed changes in the definitions of substantivity to reduce label confusion. Sweat resistant labeling would be eliminated. A sunscreen product that is water resistant should also be sweat resistant. The label of water-proof has also been proposed to be changed to very water resistant (80 minutes water protection). sunscreens should be re-applied frequently every 1 to 2 hours to maintain the labeled SPF protection from the sun, even if they are using a sweat-proof or water-proof formulation. High SPF gel-based or lip balm products are recommended for lip protection. All lip sunscreen products should be re-applied liberally and frequently at least every hour, and before and after swimming, eating, or drinking. A lotion or gel-based formulation is preferred for use with children, alcohol based formulations should be avoided due to the potential for irritation. Physical sunscreen agents (e.g., zinc oxide) are often recommended for protection of the ears and nose, areas that receive high amounts of sun exposure where sunscreens may be easily rubbed off. However, physical sunscreens may be cosmetically unappealing to many individuals and may not therefore, be used frequently enough to be helpful. Lotion or gel-based transparent sunscreens should be reapplied frequently and routinely to the nose or ears if they are used in lieu of a physical sunscreen agent such as zinc oxide.
Since most of the sunscreen products on the market today contain several active chemical sunscreens to maximize broad-band UV protection and substantivity, the selection of a sunscreen product can be primarily based on an individuals SPF need and vehicle preference.
Although sun exposure is clearly harmful to human skin, it is not necessary (or realistic) for us to become nocturnal or avoid exposure to the sun at all costs. Outdoor activities provide real physical and psychological benefits, and the use of sun protection need not diminish these.
Sunlight provides a physiological benefit by inducing vitamin D production from cholesterol precursors in the skin, an historically important means of avoiding rickets. In developed countries such as the United States, where vitamin D is readily obtained from a number of dietary sources including fortified bread, meat and dairy products, cutaneous synthesis of vitamin D should not be the principle concern driving medical recommendations about sun exposure. While people should not be discouraged from participating in outside activities, they should seek to protect themselves from the damaging effects of sunlight through the use of sunscreens, appropriate clothing, and avoiding peak UV exposure times (Tables 2 & 3).
Human exposure to solar radiation has been shown to be strongly associated with damage to the skin, ranging from sagging and wrinkles to skin cancer. Additional skin damage occurs each time a person is exposed to sunlight, and more intense exposure (sunburn) is probably associated with a non-linear exacerbation of skin damage. There appears to be no safe level of deliberate sun exposure that provides the benefits people desire (i.e., tanning, vitamin D production), without risking some incremental damage to the skin [69, 128-130]. This should not lead individuals to the conclusion that outdoor activities should be avoided or minimized, but that appropriate UV protection measures should be employed. Although UVA has been considered by some as a safe wavelength of ultraviolet, it can greatly contribute to skin aging, synergize UVB-induced damage, and contribute independently to skin cancer formation. Ultraviolet radiation in the UVB range is the principle cause of sunburn, and is thought to be the major cause of melanoma and non-melanoma skin cancer. The majority of sunscreens on the market primarily protect against UVB radiation. The Food and Drug Administration permits a sunscreen to be labeled as broad-spectrum (UVA and UVB protection) if it absorbs UV between 290-320 nm.
Recent research indicates that sunscreen use can significantly reduce the formation of pre-cancerous skin lesions. A reasonable extrapolation from human studies and animal models is that regular use of strong, broad-spectrum sunscreens and protective clothing can reduce the risk of melanoma and non-melanoma skin cancer, particularly in high risk individuals.
A few simple guidelines based on the skin type, occupation, and expected exposure can be used to help a patient select an appropriate sunscreen protection strategy. A year-round mindset should be developed regarding the use of sunscreen products for high risk individuals. The goals of sun protection should not be limited to avoidaning sunburns, but should also include the minimization of actinic damage and the risk of skin cancer associated with sun exposure.