Potent carcinogenicity of uncovered halogen lamps in hairless mice.

Uncovered halogen quartz lamps, which are potently genotoxic both in prokaryotic and human cells due to the emission of far-UV radiation (UVB and UVC), were assayed for carcinogenicity in three strains of hairless mice (SKH-1, MF-1, and C3H) of both sexes. As assessed in 5 independent experiments, no spontaneous skin tumor was observed, even after more than 2 years, in 49 animals used as unexposed controls or in 29 animals exposed to halogen lamps equipped with a common glass cover. In contrast, almost all of the 185 mice exposed to the light emitted by low-voltage (12 V) and low-power (50 W) tungsten bulbs, equipped with dichroic diffusers, contracted multiple skin tumors of various histological type, both benign and malignant. Tumors were induced over a range of illuminance levels (1,000, 3,333, 5,000, and 10,000 lux) and daily exposure times (1.5, 3, 6, and 12 h). The tumor latency times were quite short and significantly correlated with the daily exposure times, as well as with the square of the distance (46-194 cm) from the illumination source. A carcinogenic effect was even observed when exposure was discontinued well before the appearance of skin lesions. Both in vitro genotoxicity data and animal carcinogenicity data support the view that the light emitted by uncovered halogen lamps, to which an enormous number of individuals are exposed, may pose carcinogenic risks to humans. Without renouncing the benefits of this modern illumination system, UV-blocking devices should be compulsory.