Scratching and ultraviolet irradiation: an experimental animal model.

The purpose of the study was to establish a useful animal model for quantification of itching and to examine whether the wavelengths inducing itching were identical to those inducing erythema. Four groups of hairless mice were irradiated with 4 different light sources in order to provoke itch. The light sources were adjusted to give equal erythrogenic doses. The groups were treated 5 times weekly for a year. For the first 16 weeks the daily dose was 0.6 minimal erythema dose (MED) and for the following 36 weeks 1.2 MED. The severity of the itching in the 4 groups and in a control group of untreated mice was compared. The chosen parameters were the number of scratch-sequences and the summarized time of scratching during an observation period of 1 h. Ultraviolet irradiation provoked itching. Especially the wavelengths 315-330 nm were more itch-provoking than erythemogenic. The difference between the control group and a group treated with Philips TL12 combined with a Tempax filter was significant. An action spectrum of itching does not seem to be identical to the erythema action spectrum. The animal model described is usable to quantify itch but has to be simplified. Of the lamps used, Philips TL01 was the least itch-provoking lamp type and may be preferred in the treatment of itching diseases.