Quantitative assessment of phototoxicity in the skin of hairless mice.

For determining threshold levels of inflammation resulting from a phototoxic regimen, measurement of ear thickness with a hand-held micrometer was compared with assessment by eye of the reaction on the dorsa of hairless mice. The ear-measurement technique was less sensitive with respect to the minimum concentration of 8-methoxypsoralen at which phototoxicity could be detected. However this technique was more quantifiable and more objective than detection of threshold responses by eye. Changes in ear thickness were detectable over an extended period of time with a maximum increase at 16 days; return to normal thickness occurred by 35 days. Compressibility of affected ears changed during the course of measurement, but repetitive measurement of the ears did not alter the development or resolution of the inflammatory response.