Experiments with mice show that ultraviolet A (UVA) radiation does not initiate melanoma skin cancer, but ultraviolet B (UVB) does.

Dr. Edward C. De Fabo of The George Washington University Medical Center, Washington DC, and colleagues, exposed mice to light of various wavelengths. This included UVA, UVB, solar simulation, an unfiltered sunlamp, and a sunlamp filtered to remove more than 96 percent of the UVB spectrum.

Melanoma was triggered most strongly by the UVB lamp, followed by the solar simulator and the sunlamp, which both had comparable melanoma-inducing properties, De Fabo’s group reports in the September 15th issue of Cancer Research.

In contrast, mice exposed to UVA light or to the filtered sunlamp had responses no different from those of a comparison group of animals that were not exposed to any of the light sources.

“Considerable controversy exists as to which wavelengths in the sunlight spectrum initiate melanoma,” De Fabo told Reuters Health. “This paper points out clearly that UVB is the culprit whereas UVA was ineffective.”

The findings are “essential for accurately determining the melanoma risk of exposure to sunlight or suntanning lamps,” he added.

Furthermore, “By contrasting the molecular effects of UVB and UVA radiation, genes linked to melanoma initiation should be more readily identifiable.”

SOURCE: Cancer Research, September 15 2004.