Mitigation of ultraviolet-induced erythema and inflammation by para-hydroxycinnamic acid in human skin.

Objective: To evaluate whether p-hydroxycinnamic acid (pHCA) alone and in combination with niacinamide (Nam) can mitigate UV-induced erythema, barrier disruption, and inflammation.

Methods: Three independent placebo-controlled double-blinded studies were conducted on female panellists who were pretreated on sites on their backs for 2 weeks with skin care formulations which contained 0.3% or 1% pHCA with 5% Nam, 1% pHCA alone, 1.