Evaluation of Macroscopic Dermal Responses to Repeated Topical Application of 2% and 5% Niacinamide in a Rat Model (Mus musculus)
Abstract
Niacinamide is widely incorporated into topical dermatological and cosmetic formulations because it improves epidermal barrier function and skin pigmentation. However, evidence on its subacute dermal safety after repeated topical exposure at different concentrations remains limited. This study aimed to evaluate macroscopic subacute dermal responses following repeated topical application of 2% and 5% niacinamide in mice (Mus musculus). A true experimental study with a completely randomized design used 18 healthy male mice assigned to three groups: control, 2% niacinamide, and 5% niacinamide (n=6/group). Formulations were applied once daily for 14 consecutive days. Macroscopic observations were performed daily following OECD Test Guideline No. 404, covering erythema, edema, desquamation, skin lesions, ulceration, necrosis, and recovery, and were summarized descriptively. No visible dermal alterations occurred in the control and 2% niacinamide groups. The 5% niacinamide group developed mild erythema, edema, superficial desquamation, and transient skin lesions between Days 2 and 10, followed by progressive recovery with nearly complete resolution by Day 14. No ulceration or necrosis was detected in any group. These findings indicate that repeated topical application of 2% niacinamide is well tolerated, whereas 5% niacinamide induces only mild, reversible dermal irritation, supporting a favorable subacute dermal safety profile for repeated topical use.
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