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We're told to use sunscreens to protect us from skin cancer, but it appears they may not work.

Ian WishartIAN WISHART of INVESTIGATE MAGAZINE has the story

The suntan debate has taken another dramatic twist, with a new scientific study finding that while sunscreen lotion may protect us from sunburn, "there is no evidence that they protect against basal cell carcinoma or melanoma". In short, there's no evidence sunscreens prevent the serious skin cancers.

The stunning report, carried in the January issue of the journal Clinical Pharmacology and Therapeutics, published by the scientific journal Nature, is yet another blow to the New Zealand Ministry of Health's slip, slop, slap and wrap advice, and puts the Cancer Society in a tricky conflict of interest given that the Society is a major investor in a sunscreen lotion company."Safety of sunscreens is a concern," reports study author Dr Marianne Berwick, of the University of New Mexico's Cancer Centre and Department of Internal Medicine. "Sunscreen companies have emotionally and inaccurately promoted the use of sunscreens."

With global sunscreen sales in the multi-billions of dollars every year, there's money to be made in selling products that can be linked to public health campaigns. The problem for consumers and regulators is whether in fact sunscreens are worth what we are paying for them, or whether consumer fears have been overhyped. What is important to keep in mind, however, is that sunscreens do provide protection from UV damage to the skin, the kind of damage that causes premature skin ageing. If keeping skin in good condition is your prime concern, then products with sun protection factors are important.

The message from the new study is, however, don't expect sunscreens to necessarily protect you
from melanoma. Despite more than 70 years of sunscreen manufacture, the new study says proof of effectiveness is missing: "Thus far, no rigorous human evidence has shown that sunscreens prevent the major types of
skin cancer - cutaneous melanoma and basal cell carcinoma," reports the study.

"They do reduce the prevalence of actinic keratoses and recurrent squamous cell carcinoma. "With a lack of evidence that sunscreens protect against melanoma at all, have consumers been lulled into a false sense
of security, that if we slap on sunscreen we'll be OK? That's the question the new study attempts to answer.
"Sunscreens protect against sunburn, even when inappropriately applied," the study found, "even when a person applies too small an amount, and, infrequently, sunburn is generally avoided." However, Berwick's team found this
lies at the heart of the problem. We assume that because we didn't get burnt we are safe from sun damage, but apparently it isn't so: "Individuals typically use sunscreens in order to stay in the sun for longer
periods that they would otherwise and end up with high doses of UV radiation that are often sporadic or intermittent. Intermittent exposure is the strongest solar risk factor for the development of melanoma."

That's a finding that echoes two medical studies published just before Christmas (Investigate, Jan 2011 issue), that discovered people who stayed in the sun for several hours a day, regularly, were actually less likely to die of melanoma than people who only sunbathed occasionally. The studies found a strong correlation between humans getting plenty of sun and those same people effectively developing an immunity from the deadlier skin cancers. The study authors speculated that our sky-rocketing melanoma rates probably have more to do with the 20th century trend towards working in offices, out of the sun, whereas two hundred years ago most work was agricultural and in the open air. These days, most of us get intermittent - instead of regular - exposure to the sun.

As the Cancer Society wrestles with the problem that regular sun exposure actually appears to be good for you, it has altered its safety message this summer to telling people "don't get sunburnt". "Sunburn now could lead to melanoma later in life - no matter what your skin type," says the Cancer Society's "SunSmart" website. "All types of sunburn, whether serious or mild, can cause permanent and irreversible skin damage. In people with fair skin, some types of skin cancer are related to the number of severe sunburns the person has had, particularly sunburns during childhood and adolescence. Other types of skin cancer in people with fair skin tend to be related to a person's lifetime or ‘cumulative' exposure to UV radiation. "Be SunSmart and protect yourself and your family from sunburn. Slip, slop, slap and wrap." That's the current advice from the Cancer Society, but it might still be problematic, according to the Berwick study. "Unfortunately," says the new study, "some aspects of the promotion and analysis of sunscreen use are controversial. Many take the perspective that if sunburns are strongly associated with the development of melanoma, and sunscreens prevent sunburn, then sunscreens will prevent melanoma.
"However...it is likely that sunburn is a clear indicator of the interaction between excessive sun exposure and a susceptible phenotype - that is, severe solar exposure to skin unaccustomed to it - rather than a direct cause of melanoma and basal cell carcinoma."

In other words, it is not that the sunburn necessarily causes the cancer, it's just that people most susceptible to skin
cancer burn more easily. "Death from skin cancer is advertised as being avoidable with the use of sunscreens," the Berwick study reports. "This position might actually be true, but there is as yet absolutely no scientific evidence to support it...Validation of the role of sunscreens in preventing skin cancer is urgently needed."

Added to the mix is the question of Vitamin D. A growing body of scientific studies are suggesting people who get more of the sunshine vitamin are significantly less likely - a 70% reduction in some cases - to develop major tumours like breast cancer or suffer heart attacks or strokes.

Dr Berwick's latest research finds that if sunscreen were actually used correctly, it would block our ability to get Vitamin D from the sun: "If individuals actually applied sunscreen as recommended, then it is likely that routine sunscreen use would inhibit Vitamin D production. However, as noted above individuals tend to apply less [sunscreen] than is recommended, and therefore many studies show that sunscreen does not inhibit the metabolism of Vitamin D."

So where does that leave New Zealanders at the tail end of summer? If you are worried about skin damage from the sun, premature ageing and the like, then products with an SPF factor remain a crucial line of defence, supplemented by the Cancer Society's main advice to slip on clothing, a hat and sunglasses. If your primary concern is skin cancer, however, the jury is still out. There is no evidence that sunscreens protect you from the main skin cancers, and ironically the latest evidence suggests people who spend more time in the sun get greater protection against melanoma. However, that puts you back in the gun for the effects of UV radiation on skin ageing, so there's no easy answer.

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