Personally, I only use it on the roots after washing with the same series shampoo, and I use other products on the lengths. I massage it all over my head and leave it to act for a few minutes. I have dermatitis that has been flaring up in recent months (not just dandruff, I had scales) and it has helped me a lot, my skin has returned to normal very quickly, no trace of dandruff. I recommend it!