Fine Line ComboCaffine Solution: A caffeine solution, often referred to as "caffeine serum" or "caffeine eye serum," is a skincare product that contains caffeine as its main active ingredient. Caffeine is a natural compound found in coffee beans, tea leaves, and certain plants. In skincare products, caffeine is known for its potential benefits, especially when applied topically to the skin. Some common uses of caffeine solution include: Reducing Under Eye Puffiness: