The Mexican hairless dog as a model for assessing the comedolytic and morphogenic activity of retinoids.

The skin of the Mexican hairless dog is covered with comedones, and this animal therefore provides a potentially useful model to assess the comedolytic activity of topical anti-acne drugs. We treated an animal with three different formulations of tretinoin for a 14-week period, and all produced a similar clinical response. There was a striking reduction in the number of comedones, and the skin became lighter and more uniform in colour. Histological changes were similar to those reported in humans treated with tretinoin, but a novel finding was incomplete neogenesis of hair follicles. We suggest that the Mexican hairless dog may be a useful model for screening novel molecules for retinoid activity.