Of the three kinds of ultraviolet light, UV-B is of the most concern to humans. It penetrates on contact and is absorbed by the chemical bonds in DNA, snapping or tangling the bonds. This creates the distorted messages that cause cancer. The damage occurs instantly, although it may takes decades before resulting in illness.

Exposure to UV-B can also impair the body's immune system, and it can cause severe eye damage in the form of solar retinitis, basically a sunburned retina. The condition is most common among people staring at an eclipse, but it has been known to afflict sunbathers as well.

Dr. Lawrence A. Yanuzzi, a physician at Columbia Presbyterian Medical Center in New York, reported to a Congressional committee in 1988 that the previous summer he had six people come to him with solar retinitis. All six, Yanuzzi discovered, had been sunbathing on the afternoon of March 29, 1987, an unseasonably warm day that had sent people across the Northeast out of doors to parks, beaches, and backyards. What none of the six realized was that the balmy weather was accompanied by an "ozone hole" stretching from Michigan to New England. Yanuzzi's patients all had damaged their retinas gazing up at an ozone-depleted sky.

UV light also damages food crops, interfering with the way plants use sunlight to fuel their growth, and has been known to endanger fragile lower-food chain ecosystems in the ocean. It also harms the chemical bonding in inanimate materials such as roofing, shingles, painted surfaces, and rubber-based products.