Background: Adapalene is a new naphthoic acid derivative with potent retinoid and antiinflammatory properties, developed for the topical treatment of acne vulgaris.

Objective: We compare the cutaneous safety of adapalene in different gel vehicles with tretinoin 0.025% gel.

Methods: A total of 42 healthy human subjects were enrolled in two randomized, double-blind, controlled, intraindividual studies. In the first study (study A), adapalene aqueous 0.03% and 0.1% gels were evaluated for their 21-day cumulative irritation potential compared with vehicle alone, patch alone, and tretinoin 0.025% gel under occlusion. In the second study (study B), adapalene aqueous (0.03% and 0.1%) gels and adapalene alcoholic (0.03% and 0.1%) gels were evaluated for their 5-day cumulative irritation potential compared with their respective vehicles and tretinoin 0.025% gel. Transepidermal water loss (TEWL) was measured daily at each visit.

Results: In study A, adapalene had a slight irritation potential that was in the same range as the gel vehicle and the patch alone, whereas tretinoin 0.025% gel was a severe irritant. In study B, no irritation was seen with either adapalene aqueous gels or adapalene gel vehicles or patch alone. The adapalene alcoholic gels were slightly irritating, and tretinoin gel produced intense irritation reactions in the majority of subjects. TEWL increased fourfold at the tretinoin site but remained unchanged at all adapalene sites.

Conclusion: Adapalene 0.1% gel was significantly less irritating than tretinoin 0.025% gel. (J Am Acad Dermatol 1997;36:S104-9.)