A Study of Botulinum Toxin A for Ultraviolet-Induced Hyperpigmentation: A Randomized Controlled Trial.

[BACKGROUND] Ultraviolet (UV) exposure contributes to skin hyperpigmentation. Recently, botulinum neurotoxin type A (BoNT-A) showed a promising protective effect on UVB-induced hyperpigmentation in both in vitro and animal models.

[OBJECTIVE] The study aimed to investigate the preventive effect of BoNT-A against UVB-induced hyperpigmentation in human subjects.

[MATERIALS AND METHODS] A prospective, double-blinded, randomized controlled trial was performed in 15 healthy participants. Four separate square areas on the abdomen were randomly injected intradermally with different dilutions of BoNT-A (1:2.5, 1:5, 1:7.5) and normal saline (control). Two weeks after injection, hyperpigmented spots were induced by UVB irradiation at the experimental sites. The lightness index and hyperpigmentation scores from blinded physician and participants were evaluated.

[RESULTS] Fifteen participants completed the study. One week after UVB irradiation, all BoNT-A-treated sites had a significantly lower degree of hyperpigmentation than the control site in lightness index and hyperpigmentation scores from blinded physician and participants (p < .05). However, no statistically significant difference was observed between different concentrations of BoNT-A. No side effects were observed throughout the study period.

[CONCLUSION] Intradermal BoNT-A injection provided a protective effect from UVB-induced hyperpigmentation. It may be used for other hyperpigmentation disorders that are aggravated by UVB.