The clinical effect of botulinum toxin on pigmentation.

Background: Botulinum toxin injection is a common cosmetic procedure often used to treat dynamic wrinkles, but it has also been observed to have a lightening effect on the skin. It is thought that this lightening effect develops due to muscle innervation blockage; however, the change in the amount of melanin levels has not been quantified.

Method: Thirty-one patients who presented to the dermatology clinic of a tertiary hospital for botulinum toxin injection for wrinkle treatment were included in the study. A standard dose of botulinum toxin was injected to each patient's forehead, glabellar, and crow's feet region, and then the melanin index (MI) was measured with the Mexameter® MX 18 (Courage + Khazaka Electronic, Köln).

Results: After botulinum toxin treatment, a statistically significant decrease was found in the forehead and upper face MI. The upper face total baseline MI was significantly lower in the Glogau 1 group than in the Glogau 2 group (P = 0.033). The forehead 15th day MI was significantly lower in the Glogau 1 group than in the Glogau 2, 3, and 4 groups (P = 0.030).

Discussion: Botulinum toxin application to healthy skin for wrinkle treatment can cause facial skin lightening by reducing MI. It was also remarkable that this decrease was more pronounced in the forehead, which is a region that is particularly vulnerable to sun exposure, compared to other regions. Younger people, who are included in the Glogau type 1 group, may benefit more from this lightening effect.