Eflornithine HCl 13.9% cream (Vaniqa™) is a novel treatment for the management of unwanted facial hair in women. This paper reports the results of four modified open-label, within-subject vehicle-controlled studies evaluating the dermal safety of this topical treatment. In a repeated insult patch test (230 subjects), erythema with oedema occurred in 38.9% of subjects treated with eflornithine HCl 13.9% cream and 4.8% of subjects treated with vehicle cream. Challenge applications at previously untested sites following the three-week induction period produced noticeable erythema or greater on only four sites treated with eflornithine HCl 13.9% cream and one vehicletreated site. The erythema at these sites subsided substantially within 24 hours. In a three-week cumulative irritation study (30 subjects), the mean irritation score for sites treated with eflornithine HCl 13.9% cream was 1.33, compared with 0.76 at vehicletreated sites and 3.09 at positive-control (sodium lauryl sulphate-treated) sites (p < 0.001 between all three groups). In a phototoxicity study (25 subjects), irradiated sites showed either no reaction (40% of both sites treated with eflornithine HCl 13.9% cream and vehicle-treated sites), or mild erythema subsiding in all cases but one within 24 hours. No reaction was seen at non-irradiated sites. In a photocontact allergy study (30 subjects), challenge with eflornithine HCl 13.9% cream or its vehicle alone produced either no reaction or mild erythema subsiding within 24 hours at both irradiated and nonirradiated sites. No serious adverse events were reported during the studies, and the only adverse events considered related to treatment were pruritus (three subjects) and dry skin at test site (one subject). These results demonstrate that eflornithine HCl 13.9% cream does not have contact sensitising, photocontact allergic or phototoxic properties. It can cause irritation under exaggerated conditions of use. Eflornithine HCl 13.9% cream, therefore, has a favourable dermal safety profile appropriate for a topical treatment to be applied routinely.