Caffeine stimulates all the processes inside skin cells. It's very effective for reducing swelling on the face (especially great for under the eyes area). The effectiveness depends on the concentration, the more component you apply the better the effect will be.
It also tones up the skin making it look younger. It's great for dry skin because it stimulates the synthesis of cholesterol, a chemical that helps to form a protective layer on the surface of the epidermis.
Antioxidant
