The concentration of melanin is highest when the hair grows most actively from the foot. Melanin is the key factor to make the pigmentation of the hair, such that the darker the hair is, the more melanin level is the key to this method of improving hair growth efficiency. The most effective time for the IPL treatments is in the anagen phase of hair growth. In decline period hair growth stops, the pore and root shrink, and the old hair is then fallen out. Once the old hair is fallen out, a mew hair will be slowly grown in the same root. The old root remains empty until the biological cycle restarts and a new hair grows in the place of the old one.