Save your hide from UV damage. (Radiation).

Despite the increasing number of sunscreen products on store shelves, the incidence of skin cancer continues to climb. The American Cancer Society says the rate of melanoma, the deadliest type of skin cancer, more than tripled in Caucasians between 1980 and 2002. However, two recent studies have found that properly treating clothing and adding stable antioxidants to sunscreen can reduce skin damage from ultraviolet (UV) exposure.

Although experts recommend covering up in sleeves and pants to block UV rays, just how protective is clothing? In a study published in the May 2001 issue of the Journal of the American Academy of Dermatology, researchers at the New York University School of Medicine measured the UV rays that pass through different T-shirt fabrics. White T-shirt fabric was washed and dried five times under home laundry conditions. Some samples were then dyed yellow or blue with liquid fabric dye or treated with Tinosorb, a commercial UV absorber added to the wash cycle. The researchers then calculated UV protection factors (UPFs), analogous to sun protection factors, or SPFs.

Before any treatment, white T-shirts had a UPF of about 5. After five launderings, UV protection improved by 50% due to fabric shrinkage. Tinosorb boosted UV protection by 407% (to a UPF of 23.4), yellow dye by 212% (UPF 16.5), and blue dye by 544% (UPF 33.25). This shows that clothing can be treated inexpensively to block UV rays. Tinosorb is the active ingredient in the laundry additive Sun Guard[TM], says research team member David Polsky. One box of Sun Guard costs $2-3, and protection lasts several months.

But no sunscreen totally blocks UV light. The small amount of UV light that leaks through penetrates skin, creating free radicals that damage DNA and depress the immune system. To investigate where free radical damage occurs, biophysicist Kerry Hanson of the Laboratory for Fluorescence Dynamics at the University of Illinois at Urbana-Champaign peered into different depths of skin with a two-photon laser fluorescence imaging microscope. This type of microscopy shows cellular details down to the submicron level without damage to living cells. She and her colleagues are the first to use two-photon microscopy to measure UV-induced free radical generation in living skin.

Hanson exposed skin to UV rays equivalent to two hours of North American midday sun in July. She measured free radical formation before and after UV exposure with a fluorescent probe that glows when it reacts with free radicals. Hanson found that UV light generates tremendous numbers of free radicals in skin in all layers of the epidermis. But compared to bare skin, an SPF-15 sunscreen reduces free radical formation in the lower epidermis, where DNA resides, by 90%. Adding the antioxidants vitamin E acetate and a stable form of vitamin C called sodium ascorbyl phosphate to sunscreen reduces free radical formation by 95.5%. This research will appear in an upcoming issue of Photochemistry and Photobiology.

Ascorbic acid, the common form of vitamin C found in vitamin supplements and orange juice, degrades rapidly when light hits it, says Hanson. In contrast, sodium ascorbyl phosphate remains completely stable in sun and heat, she says, as does vitamin E acetate. Enzymes in the skin convert the vitamins to active forms that accumulate in skin and change free radicals into nondestructive molecules. Hanson advises checking a sunscreen's ingredient list to make sure these stable forms of vitamins C and E are there.

Hanson's research "involves some interesting new techniques," says Wayne Wamer, a research chemist at the U.S. Food and Drug Administration Center for Food Safety and Applied Nutrition in College Park, Maryland. However, the connection between UV-induced free radicals and skin cancer remains controversial. Wamer says future studies need to evaluate whether the observed reduction of free radicals by antioxidants has biological significance, such as a reduction in cell toxicity, carcinogenesis, or aging effects.