Alpecin Caffeine Shampoo C1 Achieve great things with this Caffeine Shampoo C1 from Aplecin. A natural stimulant, caffeine penetrates into hair to work directly into follicles to improve structure & stimulate growth. Leave on for 2 minutes to allow for full penetration. If left on for longer the caffeine continues to work into the scalp, leaving you with a more intense treatment. Fine, weakened hair becomes stronger & easier to style.