Scientist Rolanda Johnson Wilkerson, Ph.D., a hair and skin researcher at Procter & Gamble, explains hair growth and answers question on all of our minds: "Why can't I grow my hair long?"
The life cycle of a single strand of hair is threefold: growing, resting, shedding.
The anagen, or growth phase, is when your hair, well, grows. This lasts between two and six years, and when it’s done, that’s as long as the hair is going to get.
In the catagen, or transitional phase, which lasts a few weeks, hair growth slows down as the hair shaft starts to lift out of the follicle.
Finally, in the telogen phase, the hair is pushed out by a new hair sprouting underneath it. Your individual hairs are all at different points in this cycle, which is why you don’t periodically go bald as new shafts push out the old! Every day, about 100 get shed out and replaced by new strands.
MORE: Curly Hair Growth Chart