Rare Localized Adverse Reaction to Botulinum Toxin Type A in a Patient Without Allergic History: A Case Report

Abstract Botulinum toxin type A (BoNT-A) is widely used in aesthetic and therapeutic medicine and is considered safe. Nonetheless, rare adverse reactions can occur, even in patients with no prior allergic history. We report the case of a 50-year-old woman who developed a localized inflammatory reaction characterized by erythema, edema, vesicles, burning, and pruritus following injections in the upper face. A reactivity test with another formulation in the subcutaneous tissue of the arm produced an even more severe response, suggesting greater immune reactivity in subcutaneous tissue compared to muscle. Considering the known differences among commercial formulations, including accessory proteins and stabilizers, the test excluded the hypothesis of an allergy specific to a single brand. Standard therapies with corticosteroids and antibiotics failed to produce improvement, while ozone therapy led to significant recovery. This case emphasizes the importance of individualized follow-up and highlights the need for further studies to elucidate the immunopathological mechanisms underlying such rare hypersensitivity reactions.