Can the effect of Alpecin Caffeine Shampoo C1 be enhanced if the shampoo is left on for longer than 2 minutes?

Leaving the product on for a longer period of time also boosts caffeine absorption in the scalp. A study by a German university clinic has shown that absorption of the active ingredient increases for a period of up to 30 minutes when the product is left on the scalp. After that, penetration via the skin surrounding the follicles has increased to such an extent that additional caffeine availability is ensured for up to about eight hours. If you leave the product on your scalp for longer than 2 minutes, you should check your scalp type and scalp condition. Depending on your scalp's sensitivity, leaving the product on for excessively long can result in temporary redness.