Lifetime topical application of tretinoin to hairless mice.

The discovery that topical tretinoin can reverse some or the effects or photodamage may lead to its chronic application. Examination or long-term effects was or interest. Three groups of hairless mice (age 6-8 weeks) were treated dorsally with 1) tretinoin (0.025%), 2) cream vehicle, 3) sham treatment. Applications were 3 times weekly and continued for up to 2 years until all mice were sacrificed or had died. Biweekly examinations showed no sign of retinoid toxicity, with growth and longevity similar in all groups. Tretinoin-treated skin was smooth and pink, resembling that of younger mice