This Caffeine Shampoo contains caffeine that can help to stimulate hair growth directly at the roots. A daily wash with Alpecin C1 shampoo immediately provides the hair roots with the activating ingredient. Alpecin Caffeine shampoo Hair Energizer is detectable after being left on for as little as 120 seconds. If left on longer, more caffeine will be absorbed into the scalp. Alpecin Caffeine penetrates even though the shampoo is rinsed out. In just a short time (120 sec.), caffeine travels along the hair shaft directly into the hair follicles.