Persistent Hyperpigmentation Following Coretox Injection: A Review of Adverse Events Associated with Polysorbate 20

Postprocedural hyperpigmentation is a rare but concerning complication after botulinum toxin type A injections. In 2024, 3 patients developed persistent facial hyperpigmentation following Coretox administration in the glabellar and forehead regions. This case series characterizes the clinical course, imaging findings, and hypothesized mechanisms underlying this reaction. Three female patients received Coretox injections using standard aesthetic techniques, including subdermal injections in the forehead and periorbital regions and intramuscular injections in the glabellar region. Serial clinical photographs and QuantifiCare LifeViz imaging-including cross-polarized, ultraviolet-filtered, and hemoglobin-filtered modes-were performed from baseline through follow-up. Medical histories, sun exposure, skincare routines, and concurrent medications were reviewed. No patients reported recent use of photosensitizers, active dermatitis, or excessive ultraviolet exposure. All 3 cases exhibited localized hyperpigmented macules at injection sites, appearing 2-3 weeks postprocedure. QuantifiCare imaging demonstrated elevated melanin and hemoglobin signal intensity in affected areas. Although pigmentation lightened slightly over 2-3 months, the discoloration persisted beyond 1 year in all cases as of October 2025. Exosome-based treatment, Rejuran injection, and laser therapies were attempted without significant improvement. Approximately 1,400 vials of Coretox have been used by the author since 2019, with all three pigmentation events linked to batch E622080A (June 28, 2024). This is the first report to document persistent facial hyperpigmentation following Coretox injection, using serial imaging analysis. Although the pathogenesis remains unclear, polysorbate 20-a stabilizer replacing human serum albumin-may act as a trigger in susceptible individuals. Early recognition, patient counseling, and photoprotection are recommended. Further investigation into excipient-induced pigmentary changes is warranted.