The hair's life cycle

What does the hair cycle look like?

The hair’s growth is cyclical in nature and is characterized by phases of growth, regression and regeneration. This is referred to as the hair cycle. Each cycle is comprised of three main phases.

• The anagen phase is the hair’s growth phase and lasts two to six years. It concerns about 85% of the hair. The hair shaft is produced by the hair follicle during this phase. The characteristics of the hair follicle (size) and hair shaft (length) depend on the volume and number of cells found in the dermal papilla. During the anagen phase, fibroblasts in the dermal papilla release signals that trigger the proliferation, migration and differentiation of the matrix cells located at the base of the follicle to form the hair shaft. Over the course of this phase, hair grows approximately 1 cm per month.
• The catagen phase is the hair’s regression or degeneration phase and lasts two to three weeks. During this transitional phase, the bulb cells go into apoptosis, thus causing the regression of the lower part of the hair follicle. During this time, the bulb is inactive and the hair stops growing.
• The telogen phase is the rest phase (less than 10% of hairs are concerned), in terms of activation and proliferation. No production of the hair shaft is observed during this stage. It is during this two- to three-month hair loss phase that the dead hair falls out, having been pushed out by a new hair entering into another anagen phase.

The hair cycle: True or false

One year = one hair cycle

False- We know that, in its lifetime, the hair follicle undergoes 25 to 30 cycles on average. This is the hair’s vital cycle. Luckily, however, the number of hairs that grow is always well above the number of hairs that fall out: on a normal scalp with about 100,000 hairs, 86% of the hairs are in the anagen, or growth, phase.

The duration of the hair cycle may change

True- The hair cycle may speed up due to an excess of male hormones, androgens. This phenomenon disrupts normal hair growth. Because the hair is growing faster than usual, it becomes depleted and thinner, until it falls out permanently. This is androgenetic alopecia, a chronic hair loss (lasting more than three to six months) and is difficult to reverse. It should not be confused with seasonal hair loss, which is occasional (acute telogen effluvium) and has a more positive outcome, or with age-induced alopecia, which is caused by a reduction in the hair’s diameter associated with physiological aging of the hair.

Does the lunar cycle have an impact on hair growth?

Throughout this conventional hair cycle, the lunar calendar is thought to have an influence on hair growth. The position of the moon in the sky could promote or discourage hair follicle growth. Although this phenomenon has yet to be proven scientifically, many specialists are actively exploring the possibility.