Look for serums with a concentration of vitamin C between 10% and 20%. Lower than that might not bring the promised benefits, and higher could irritate your skin without bringing any additional value.

Dab on vitamin C cream or serum after you wash your face and before you apply moisturizing lotion. It could sting or make your skin red at first, but that should go away if you keep using it. Test any new products on a small area before applying them to your whole face.

Go easy if you want to use a vitamin C serum along with other acidic skin care products like retinol. Together they could irritate your skin. Consider using them on alternating days rather than at the same time.

Keep your vitamin C serum away from light and air — both can hurt the ingredients. Choose a product in a dark-colored container to protect it. Seal the lid tightly and stash it somewhere cool, dark, and dry.