Dr.Althea's Vitamin C Boosting Serum makes a trade that most people should take.

Pure L-ascorbic acid is the most potent and best-studied form of vitamin C. It also stings, oxidises quickly, and is abandoned by a large proportion of the people who buy it - usually within a month. A serum sitting unused in a drawer has an effectiveness of zero regardless of its concentration.

This uses a stabilised vitamin C derivative instead. Less potent per application, but no sting, no oxidising, and therefore a product people actually finish. For an ingredient that works through consistency over months rather than intensity in a week, that is the better bargain.

Niacinamide provides a second brightening route while supporting the barrier, and hyaluronic acid offsets the mild dryness sustained brightening causes.

Use once or twice daily after cleansing, before moisturiser. If you use it in the morning, sunscreen over the top is essential - brightening actives and UV work directly against each other.