The hair follicle (also called hair root) is located beneath the scalp and has to function properly in order to maintain healthy hair. A hair follicle is about 4 to 6 millimeters in length. Each follicle produces one to four hair shafts, each being about 0.1 millimeter in size. So, these hair shafts are very small.
The hair does not grow in individual strands, but develops from the scalp in groups of one to four and sometimes even five or six strands. Hair follicles are arranged in naturally occurring groups, called follicular groups.
About 90% of your hair is actively growing. Normally, the hair grows at a rate of about 1.25 cm per month. The catagen phase is the transition phase between the growth and resting phase. During this phase, the hair follicle withdraws and detaches from the hypodermis (where it gets its nutrients). The hair root disappears and the root end turns into a knot-like shape.
About 1 percent of the hair is in the catagen phase. This phase generally lasts about one to two weeks. The rest of the hair is not actively growing and is in the resting phase, also called the telogen phase. This phase lasts about three to five months with a healthy scalp.
People lose about 100 hairs per day. The presence of much more hair on your brush, in the sink in your bath can be a first sign of excessive hair loss.