When you cut your hair, it usually grows fast to a certain length and then stops. Now how on earth does either the follicle or the hair itself know how long a hair is, and what controls the rate of growth?

McGruff

Normal Hair Growth All follicles repeatedly cycle through the following 3 stages. 1. Anagen Stage (growth) The new hair grows from the base of the follicle. This growth phase usually lasts for a number of years and results in a full-grown hair. 2. Catagen Stage (resting) During this stage the hair stops growing and the hair root shrinks. The base of the follicle breaks dow and the hair moves upward in the follicle, wawy from the root and the blood vessel supplying it with nutrients. 3. Telogen Stage (re-growth) The mature hair is now only loosely anchored to the hair root. It usually falls out after a few months or is pushed out by the next hair growing up below it. After birth, different hormones affect the follicle allowing growth or causing hair follicles to move into the resting (telogen) phase. A hormone called dihydrotestosterone (DHT) a product made from testosterone, acts on the hair follicle causing growth to slow and ultimately stop. DHT only works on certain hair follicles that have the genetic predisposition to be shut off. Feb 24 02, 12:02 PM

Gnomon

What all that means is that a hair will keep growing until it reaches a particular length, then it will fall out and another one will grow from the same spot. The hair root grows for a certain length of time, not to a certain length, so if you cut the hair, it will not regrow to the same length. Feb 24 02, 5:17 PM