Trichloroacetic acid model to accurately capture the efficacy of treatments for postinflammatory hyperpigmentation

Postinflammatory hyperpigmentation (PIH) occurs following cutaneous injury and is common following resolution of acne especially in patients with skin of color. The objective of this study was to further validate a trichloroacetic acid (TCA)-induced PIH model and compare it to acne-induced PIH using topical bakuchiol, a botanical extract that has been shown to have antimicrobial, anti-inflammatory, antioxidant, and antiacne properties. A prospective, non-randomized clinical trial was conducted on subjects with skin phototypes IV–VI with a history of acne-induced PIH. Subjects applied bakuchiol or vehicle cream twice daily to 2 acne-induced and 2 TCA-induced PIH lesions for 28 days with a third lesion serving as a control in each group. Degree of improvement was defined as the change in the Investigator Global Assessment (IGA) score over 28 days of treatment. Twenty subjects (6 males, 14 females) completed the study. For TCA-induced PIH sites, there was a statistically significant (p < 0.05) degree of improvement with bakuchiol treatment (− 0.50 ± 0.18) compared to vehicle (0.05 ± 0.15) and control (− 0.06 ± 0.17). For acne-induced PIH, there was a greater degree of improvement for bakuchiol (− 1.06 ± 0.23) when compared to vehicle (− 0.56 ± 0.16) and control (− 0.69 ± 0.18); however, statistical significance was not reached (p > 0.05). TCA-induced PIH sites were uniform in size and pigment intensity thereby allowing better comparison among sites. This emphasizes the relevance of using this model for PIH which may help reduce the barriers in clinical trials and help improve access to treatments for patients who suffer from PIH. The results suggest that topical bakuchiol may decrease the severity of PIH.