Abstract: Objective To investigate the skin reactions induced by to pical 0.1% tretinoin and its vehicle in mice. Methods 0.1% tretinoin and its vehicle were applied separately on mice backs,once a day for 30 days.The skin reactions,including erythema and scaling,were observed macroscopically and meas ured by biological instruments. Results Macroscopically the skin reactions of erythema and scaling induced by topical tretinoin occurred on day 3 after application,reached its peak on day 6 and disappeared on day 12,and neither erythema nor abnormal scaling appeared in spite of continuing application until day 30.The erythema value measured was enhanced significantly on day 1 after application,reached its peak on day 6,maintained until day 9 and became normal on day 11.From then to day 30,it maintained at the normal level.The scaling value measu red enhanced significantly on day 3 after application,reached its peak on day 9 and became normal on day 27.Topical application of the vehicle induced neither skin reaction nor any change of erythema and scaling value. Conclusions Topical application of 0.1% tretinoin induces skin reaction characterized by erythema and scaling.The reaction,transient but not related to the vehicle,experiences a process of "occurrence-peak-disappearance".

Key words: Tretinoin, Skin irritancy tests, Administration, cutaneo us, Animal testing alternatives