| A panel of experts has warned that the risks of passive sunburn are increasing steadily as the cosmetics industry researches more and more sophisticated sun-blocking technologies.
Passive sunburn occurs when a sunbather wears a cream with a higher sun protection factor (SPF) than his or her neighbours. Ultra-violet rays from the sun bounce off the protected skin and onto that of the other bathers, whose lower-SPF creams are unable to shield them adequately.
"Until recently, sun creams were just not effective enough to constitute a major problem," explains Sheila Hague of the Willliam Harvey Research Institute. "But today's strongest creams are so effective that, ironically, they pose a significant danger to people not wearing them while protecting those who do."
A related, though much rarer, danger is a phenomenon known as ultraviolet resonance (UVR), which can happen when many sunbathers are wearing suncream with the same SPF. Whereas with passive sunburn a reflected ray is absorbed by under-protected skin, in UVR a ray bounces continually from one bather to another, and if the distance between reflections happens to be a multiple of the ray's wavelength it will acquire more and more energy as it resonates.
"We last observed UVR at the crowded Lassithi beach resort in Crete," Hague tells us. "We tracked a single ultra-violet ray across 41 sunbathers over 15 minutes. It had acquired a tremendous amount of energy by this time, and tragically when the ray finally escaped the loop it hit and killed a small dog belonging to a local man. We should be thankful it wasn't a person who lost their life, but I hope that the incident drives home the message that passive sunburn and UVR are threats to be taken seriously."
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