ZURICH -- Wearing protective clothing is better than using sunscreens to prevent skin cancer and hold off the aging effects of solar rays, said investigators here.
ZURICH, May 4 -- Wearing protective clothing is better than using sunscreens to prevent skin cancer and hold off the aging effects of solar rays, according to investigators here.
So said the authors of a review article, who've taken their recommendations right down to the wet T-shirt level.
Although nothing blocks harmful solar rays like staying indoors, wearing tightly woven, thick garments and a hat is the next best thing, advised Stephan Lautenschlager, M.D., of the Triemli Hospital, and colleagues.
After an extensive literature review published online in The Lancet, the researchers noted that not all textiles provide equal protection. Contrary to common wisdom, they noted, a light-colored cotton shirt provides only limited ultraviolet protection -- equivalent to a sun protection factor (SPF) of only 10. SPFs range from the least protective 2 to 64.
Laboratory testing of UV transmission through fabrics showed that a large number of factors are at play, including thickness, weight, color, type, and porosity of the fabric. Even wetness matters: A T-shirt worn into the water to ward off the sun while swimming is less effective wet than when it was dry.
Thus, the researchers said, ideal protective garments are dry, dark and unbleached, tightly woven and thick, made of denim, wool, or a synthetic material such as polyester. Less effective are light-colored, loosely woven, thin fabrics such as cotton, linen, acetate, or rayon.
And garments that have shrunk after washing (making them denser) are better at stopping harmful rays than stretched textiles and those that have been bleached.
The use of appropriate clothing and garments specially manufactured to protect against UV radiation provided excellent protection, the researchers said. However, they added, there are conflicting reports as to whether clothing can prevent melanocytic nevi, strong predictors of subsequent malignant melanoma.
The researchers noted, however, that because clothing protection seems to be "unacceptable in our global, outdoor society," people should be advised as to how to make the best use of sunscreens.
Several studies have shown a reduction in the number of actinic keratoses and squamous cell carcinomas, but not basal cell cancers among careful and regular sunscreen users, the authors said. Although many studies have shown protection against the aging effects of sun, whether sunscreen stops melanoma remains controversial, they said.
Addressing a possible harm from long-term use of sunscreens on vitamin D levels, the researchers concluded that clinical studies have found little or no effect on vitamin D levels, and did not induce osteoporosis or secondary hyperparathyroidism.
Only low levels of exposure to ultraviolet radiation are necessary to avoid vitamin D deficiency. Exposure of the hands, arms, and face two or three times a week to a third to a half of the erythemal dose (about five minutes for an adult in Boston at noon in July) is more than adequate, the investigators said.
Discussing the self-tanning product dihydroxyacetone, the researchers said, it has generally not been considered to be an effective sunscreen. However, there is some evidence to suggest that it gives at least a little protection, with a low SPF of 2 to 3 and a durability of five to six days.
The protective nature of the compound has been confirmed in a hairless mouse study that showed a delay of broad-spectrum ultraviolet carcinogenesis. The compound could therefore function as a base for other protective measures, the researchers wrote.