A quantitative study of the melanogenic effect of multiple suberythemal doses of different ultraviolet radiation sources.

The melanogenic potential of multiple suberythemogenic doses of 6 different ultraviolet (UV) sources was investigated. The UV sources emitted different amounts of UVA and UVB. The backs of 12 volunteers were exposed to the 6 UV sources 10 times during 4 weeks. Every volunteer was exposed to the same suberythemogenic dose (0.75 basic minimal erythema dose) of each of the UV sources. The changes in pigmentation and minimal erythema dose of the UV exposed test sites were registered during the 10 sessions. Three UVA sources with a low emission in the UVB area (0.2-3.1%) had a high melanogenic potential. Two UVB sources (UVB emission 74.3% and 94.5%) were unable to induce a significant increase in skin pigmentation. The 3 UVA sources with a low UVB output increased skin pigmentation significantly better than a UVA source with a UVB output of 6.9%. All 6 lamps were able to increase photoprotection significantly. The increase in photoprotection was not significantly different between any of the 6 UV sources. This study shows that, if humans are exposed to equally suberythemogenic doses of different types of UV radiation, then radiation obtained from UVA sources greatly enhances melanogenesis, whereas UVB radiation sources are unable to induce pigmentation.