COSRX Niacinamide 15% Serum

The COSRX Niacinamide Serum contains 15% niacinamide, which is a higher concentration than most mainstream options like The Ordinary's 10% Niacinamide + Zinc. The serum also includes EGCG (epigallocatechin gallate) from green tea as a soothing antioxidant. At 15%, it is formulated for visible brightening and hyperpigmentation correction.

While older research suggested niacinamide and vitamin C should not be layered, more recent dermatological guidance indicates they can be used together safely in most formulations. However, at 15% concentration, the COSRX serum is potent, and combining it with retinol or strong acids in the same routine may increase irritation risk. Many users alternate niacinamide and retinol on different nights or use niacinamide in the morning and retinol at night.

Niacinamide at 15% is well-documented for fading post-inflammatory hyperpigmentation (the flat dark marks left after acne heals) by inhibiting melanin transfer. The EGCG in the formula also provides anti-inflammatory benefits that can help calm active redness. However, niacinamide will not improve atrophic or pitted acne scarring, which requires treatments like microneedling or chemical peels.

The serum is formulated to be suitable for most skin types, including oily and combination skin, as niacinamide helps regulate sebum production in addition to brightening. Sensitive skin users should patch test first, as 15% is a relatively high concentration that can cause tingling or flushing in some individuals. The Korean formulation philosophy of the product means it is designed to layer well within multi-step routines.