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Sunscreens: Do they cause skin cancer?

by Hans R. Larsen, MSc ChE

In 1991 Professor Johan Moan of the Norwegian Cancer Institute made an astounding discovery. He found that the yearly incidence of melanoma in Norway had increased by 350% for men and by 440% for women during the period 1957 to 1984. He also determined that there had been no change in the ozone layer over this period of time. He concludes his report in the British Journal of Cancer by stating "Ozone depletion is not the cause of the increase in skin cancers"(1).

SKIN CANCER

There are three major forms of skin cancer.

BASAL CELL CARCINOMA is the most common form of skin cancer. It occurs most frequently in men who spend a great deal of time outdoors and primarily produces lesions on the head and neck(2). Basal cell carcinoma rarely spreads throughout the body but can invade neighbouring bone and nerves(3).

SQUAMOUS CELL CARCINOMA is the second most common skin cancer. It primarily affects people who sunburn easily, tan poorly, and have blue eyes and red or blonde hair. Squamous cell carcinoma most commonly develops from actinic keratoses and can metastasize if left untreated. Squamous cell carcinoma of the lip is 12 times more common among men than among women(4).

MALIGNANT MELANOMA is the rarest form of skin cancer but is the most deadly. It affects the cells which produce melanin and seems to be more prevalent among city-dwellers than among people who work out-of-doors. It does not necessarily occur on sun-exposed areas of the body and is thought to be linked to brief, intense periods of sun exposure and a history of severe sunburn in childhood or adolescence. Malignant melanoma metastasizes easily and is often fatal if not caught in time(2,5).

The skin cancer epidemic is a worldwide phenomenon. In 1978 there were approximately 480,000 cases of non-melanoma skin cancer in the United States alone. This is expected to rise to over one million in 1994(6). Malignant melanoma is growing at a rate of 7% per year in the United States. In 1991 cancer experts estimated that there would be about 32,000 cases during the year of which 6,500 would be fatal(7). In Canada melanoma incidence rose by 6% per year for men and by 4.6% per year for women during the period 1970- 1986(8). Australia has the highest melanoma rate in the world. For men the rate doubled between 1980 and 1987 and for women it increased by more than 50%(9). It is now estimated that by age 75 two out of three Australians will have been treated for some form of skin cancer(10).

If the ozone layer has not yet changed significantly except at the poles, then what is causing the enormous increase in skin cancer?

The sunscreen connection

The Australian experience provides the first clue. The rise in melanoma has been exceptionally high in Queensland where the medical establishment has long and vigorously promoted the use of sunscreens. Queensland now has more incidences of melanoma per capita than any other place. Worldwide, the greatest rise in melanoma has been experienced in countries where chemical sunscreens have been heavily promoted(11).

Drs. Cedric and Frank Garland of the University of California are the foremost opponents of the use of chemical sunscreens. They point out that, although sunscreens do protect against sunburn, there is no scientific proof that they protect against melanoma or basal cell carcinoma in humans(11). There is, however, some evidence that regular use of sunscreens helps prevent the formation of actinic keratoses, the precursors of squamous cell carcinoma(12).

The Garland brothers strongly believe that the increased use of chemical sunscreens is the primary cause of the skin cancer epidemic. They emphasize that people using sunscreen tend to stay longer in the sun because they do not get a sunburn - they develop a false sense of security(7). Chemical sunscreens are formulated to absorb UVB radiation, they let most of the UVA rays through(7). UVA rays penetrate deeper into the skin and are strongly absorbed by the melanocytes which are involved both in melanin production (sun tanning) and in melanoma formation(11). UVA rays also have a depressing effect on the immune system(13).

ULTRAVIOLET RADIATION

UVA rays constitute 90-95% of the ultraviolet light reaching the earth. They have a relatively long wavelength (320-400 nm) and are not absorbed by the ozone layer. UVA light penetrates the furthest into the skin and is involved in the initial stages of sun tanning. UVA tends to suppress the immune function and is implicated in premature aging of the skin(2,13,14).

UVB rays are partially absorbed by the ozone layer and have a medium wavelength (290-320 nm). They do not penetrate the skin as far as the UVA rays do and are the primary cause of sunburn. They are also responsible for most of the tissue damage which results in wrinkles and aging of the skin and are implicated in cataract formation(2).

UVC rays have the shortest wavelength (below 290 nm) and are almost totally absorbed by the ozone layer. As the ozone layer thins UVC rays may begin to contribute to sunburning and premature aging of the skin(2).

All forms of ultraviolet radiation are believed to contribute to the development of skin cancer(2).

Most chemical sunscreens contain from 2 to 5% of benzophenone or its derivatives (oxybenzone, benzophenone-3) as their active ingredient. Benzophenone is one of the most powerful free radical generators known to man. It is used in industrial processes to initiate chemical reactions and promote cross-linking(15). Benzophenone is activated by ultraviolet light. The absorbed energy breaks benzophenone's double bond to produce two free radical sites. The free radicals desperately look for a hydrogen atom to make them "feel whole again"(15). They may find this hydrogen atom among the other ingredients of the sunscreen, but it is conceivable that they could also find it on the surface of the skin and thereby initiate a chain reaction which could ultimately lead to melanoma and other skin cancers. Researchers at the Harvard Medical School have recently discovered that psoralen, another ultraviolet light-activated free radical generator, is an extremely efficient carcinogen. They found that the rate of squamous cellcarcinoma among patients with psoriasis, who had been repeatedly treated with UVA light after a topical application of psoralen, was 83 times higher than among the general population(16).

The benefits of sunlight

Some scientists believe that UV light causes skin cancer through the combined effect of suppression of the immune system and damage to DNA(10,17). Exposure to UV light is, however, not all bad. Most of the body's vitamin D supply, about 75% of it, is generated by the skin's exposure to UVB rays(18). Using a sunscreen drastically lowers the cutaneous production of vitamin D3(19). A low blood level of vitamin D is known to increase the risk for the development of breast and colon cancer and may also accelerate the growth of melanoma(18,19,20).

Dr. Gordon Ainsleigh in California believes that the use of sunscreens causes more cancer deaths than it prevents. He estimates that the 17% increase in breast cancer observed between 1991 and 1992 may be the result of the pervasive use of sunscreens over the past decade(20). Recent studies have also shown a higher rate of melanoma among men who regularly use sunscreens and a higher rate of basal cell carcinoma among women using sunscreens(11,21).

Dr. Ainsleigh estimates that 30,000 cancer deaths in the United States alone could be prevented each year if people would adopt a regimen of regular, moderate sun exposure(20).

Although the medical establishment still strongly supports the use of sunscreens there is a growing consensus among progressive researchers that the use of sunscreens does not prevent skin cancer and, as a matter of fact, may promote skin cancers as well as colon and breast cancer.

The bottom line

So what should you do to protect yourself as much as possible against these cancers? Summarizing current research the following recommendations appear reasonable:

DO NOT rely on the use of sunscreens to protect you against skin cancer.

DO NOT try to get a tan by visiting a tanning studio. The rays from their UV lamps are extremely harmful and the tan produced does not have the protective effect of a sunlight-induced tan(2,7).

DO try to develop a moderate natural suntan unless you have extremely sensitive skin and burn easily. Regular and moderate unprotected sun exposure in the early morning or late afternoon will help maintain a protective tan and keep your vitamin D stores at an optimum level(20).

DO wear protective clothing and a wide-brimmed hat when you are outside. Avoid sun exposure between 10 AM and 3 PM if at all possible. Remember that UV rays, particularly UVA, are present even on cloudy days(7).

DO wear sunglasses that filter out 100% of the ultraviolet light to protect yourself against the development of cataracts(7).

DO remember that sunlight is strongly reflected from sand, snow, ice, and concrete and can increase your direct sunlight exposure by 10 to 50%(2).

DO make sure you get enough vitamin D3 and beta-carotene, if necessary through supplementation. Recent research has shown that taking 30 mg of beta-carotene a day protects against the suppression of the immune system by UVA rays(13).

DO make sure to supplement your diet with antioxidants. Dr. Abram Hoffer in Victoria, Canada recommends that vitamin C, vitamin E, and selenium be used as a protection against the damages of excessive ultraviolet radiation. He suggests daily dosages of 3 grams or more of vitamin C, 800 IU of vitamin E, and 200 micrograms of selenium (l-selenomethionine)(22). Vitamins C and E also protect against cataract formation(23,24).

DO cut down on the fat in your diet. Recent research has shown that patients with non-melanoma skin cancers can reduce their risk of developing additional actinic keratoses (precursors to skin cancer) by switching to a low fat diet(25).

SUNSCREENS

Sunscreens are designed to protect against sunburn (UVB rays) and generally provide little protection against UVA rays. They come in two forms:

CHEMICAL SUNSCREENS contain chemicals such as benzophenone or oxybenzone (benzophenone-3) as the active ingredient. They prevent sunburn by absorbing the ultraviolet (UVB) rays(2).

PHYSICAL SUNSCREENS contain inert minerals such as titanium dioxide, zinc oxide, or talc and work by reflecting the ultraviolet (UVA and UVB) rays away from the skin(2).

A sunscreen with a SPF of 15 filters out approximately 94% of the UVB rays. One with a SPF of 30 filters out 97%. The SPF applies for UVB rays only. The protection provided against UVA rays in chemical sunscreens is about 10% of the UVB rating(26).

DO wear a physical sunscreen with a SPF of 15 if you absolutely must be out in the sun for extended periods of time(22). Physical sunscreens containing titanium dioxide, zinc oxide, or talc work by reflecting the UV radiation rather than by absorbing it. Sunscreens are tested by using artificial UV light and a screen with a SPF of 30 is not twice as effective as one with a factor of 15(17). Also, reapplying sunscreen during the day does not extend the period of protection. Even "broad-spectrum" sunscreens are not very good in filtering out UVA rays(26). A natural suntan is probably more effective.

DO see your healthcare provider if you spot any unusual moles or growth on your skin - particularly if they are irregular in shape, bleed, itch, or appear to be changing. Most skin cancers can be cured if caught in time(27).

The saga of sunscreens and skin cancer is far from over. Research is continuing and new findings are being published at an accelerated pace. But until we know the whole story, it would seem prudent to take precautions based on what we do know.

REFERENCES

Moan, J. & Dahlback, A. The relationship between skin cancers, solar radiation and ozone depletion. British Journal of Cancer, Vol. 65, No. 6, June 1992, pp. 916-21

Harmful effects of ultraviolet radiation. Journal of the American Medical Association, Vol. 262, No. 3, July 21, 1989, pp. 380-84

Haynes, Harley A. Primary cancer of the skin. Harrison's Principles of Internal Medicine, McGraw-Hill, 7th ed., 1974, pp. 2024-25

Hacker, Steven M. & Flowers, Franklin P. Squamous cell carcinoma of the skin. Postgraduate Medicine, Vol. 93, No. 8, June 1993, pp. 115-26

Lee, John A.H. The relationship between malignant melanoma of skin and exposure to sunlight. Photochemistry and Photobiology, Vol. 50, No. 4, 1989, pp. 493-96

Miller, Dena L. & Weinstock, Martin A. Nonmelanoma skin cancer in the United States: incidence. Journal of the American Academy of Dermatology, Vol. 30, No. 5, Pt. 1, May 1994, pp. 774-78

Skolnick, Andrew A. Revised regulations for sunscreen labelling expected soon from FDA. Journal of the American Medical Assocation, Vol. 265, No. 24, June 26, 1991, pp. 3217-20

Statistics Canada, Canadian Cancer Statistics 1991.

Reynolds, Tom. Sun plays havoc with light skin down under. Journal of the National Cancer Institute, Vol. 84, No. 18, September 16, 1992, pp. 1392- 94

Ozone depletion and health. The Lancet, December 10, 1988, p. 1377

Garland, Cedric F., et al. Could sunscreens increase melanoma risk? American Journal of Public Health, Vol. 82, No. 4, April 1992, pp. 614-15

Dover, Jeffrey S. & Arndt, Kenneth A. Dermatology. Journal of the American Medical Association, Vol. 271, No. 21, June 1, 1994, pp. 1662-63

Fuller, Cindy J., et al. Effect of beta-carotene supplementation on photosuppression of delayed-type hypersensitivity in normal young men. American Journal of Clinical Nutrition, Vol. 56, 1992, pp. 684-90

Fitzpatrick, T.B. & Haynes, H.A. Photosensitivity and other reactions to light. Harrison's Principles of Internal Medicine, McGraw-Hill, 7th ed., 1974, pp. 281-84

Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 13, 3rd ed., 1981, pp. 367-68

Stern, Robert S. and Laid, Nan. The carcinogenic risk of treatments for severe psoriasis. Cancer, Vol. 73, No. 11, June 1, 1994, pp. 2759-64

Wright, Brett. Sunscreens and the protection racket. New Scientist, January 22, 1994, pp. 21-2

Garland, Frank C., et al. Geographic variation in breast cancer mortality in the United States: a hypothesis involving exposure to solar radiation. Preventive Medicine, Vol. 19, 1990, pp. 614-22

Koh, Howard K. & Lew, Robert A. Sunscreens and melanoma: implications for prevention. Journal of the National Cancer Institute, Vol. 86, No. 2, January 19, 1994, pp. 78-9

Ainsleigh, H. Gordon. Beneficial effects of sun exposure on cancer mortality. Preventive Medicine, Vol. 22, February 1993, pp. 132-40

Garland, Cedric F. et al. Effect of sunscreens on UV radiation-induced enhancement of melanoma growth in mice. Journal of the National Cancer Institute, Vol. 86, No. 10, May 18, 1994, pp. 798-801

Goodall, John & Hoffer, Abram. Protection against ultraviolet radiation. Canadian Medical Association Journal, Vol. 147, No. 6, September 15, 1992, pp. 839-40

Robertson, J.M., et al. Vitamin E intake and risk of cataracts in humans, Annals of the New York Academy of Science, Vol. 570, 1989, pp. 372-82

Knekt, Paul, et al. Serum antioxidant vitamins and risk of cataracts. British Medical Journal, Vol. 305, December 5, 1992, pp. 1392-94

Black, Homer S., et al. Effect of a low-fat diet on the incidence of actinic keratosis. The New England Journal of Medicine, Vol. 330, No. 18, May 5, 1994, pp. 1272-75

Kaidbey, Kays & Gange, R. William. Comparison of methods of assessing photoprotection against ultraviolet A in vivo. Journal of the American Academy of Dermatology, Vol. 16, No. 2, Pt. 1, February 1987, pp. 346-53

McDonald, Charles J. Status of screening for skin cancer. Cancer (supplement), Vol. 72, No. 3, August 1, 1993, pp. 1066-70