Niacinamide — the vitamin B3 in so many K-beauty serums

Niacinamide is a type of vitamin B3. Cleveland Clinic explains that your body makes it from niacin or from the amino acid tryptophan, but in skincare you apply it on the skin. It is found in cleansers, serums, moisturizers and even some sunscreens. In Korean it is written 나이아신아마이드.

Cleveland Clinic lists several possible benefits: it may support the skin's lipid barrier, ease inflammation and redness, help skin look smoother with less visible pores, and help regulate oil. It says nothing has been proven to reduce actual pore size.

Some research suggests formulas with 5% niacinamide can help lighten dark spots, and it says a topical product may improve fine lines and wrinkles. Brands such as Anua combine niacinamide with other brighteners; read those claims as the brand's description, not a guarantee.

Cleveland Clinic says most products contain 5% niacinamide or less, and that people with sensitive skin should start slowly with a low concentration. It can be used once or twice a day after gentle cleansing. It pairs well with moisturizers with ceramides and hyaluronic acid, and you can also find it in sunscreens, but don't use too many niacinamide products at once.

A 10% serum like Anua's is above that "5% or less" range, so start slowly, as Cleveland Clinic advises for sensitive skin, and add it as the only new product.

Cleveland Clinic calls niacinamide generally gentle and safe, with rare side effects: an allergic reaction, itching, a mild burning feeling or redness. Its advice is a patch test on your forearm for 24 hours. The AAD's longer method is a quarter-sized spot twice a day for seven to 10 days.