Clinical effects of long-term therapy with topical tretinoin and cellular mode of action.

In a double-blind, placebo-controlled study, 0.1% topical tretinoin reduced the effects of photo-ageing maximally after 10 months, with no further improvements if treatment was continued until 22 months. Topical tretinoin induced epidermal hyperplasia, compaction of the stratum corneum and the deposition of ultrastructurally visible collagen fibrils in the papillary dermis. It also reduced the number and activity of melanocytes, and possibly induced angiogenesis. An Alcian Blue-positive glycosaminoglycan-like substance was detected in the stratum corneum of tretinoin-treated skin and mitoses were significantly increased. The cellular changes brought about by tretinoin may, in part, be the basis for the clinical improvement in photo-aged skin brought about by tretinoin.