The cycles of activity within a hair follicle consist of two primary stages: the active stage, where new hair is produced, and the resting stage, during which cell activity diminishes and halts. The active stage endures for a few years until the hair achieves its maximum length. When the resting phase takes place, the hair expires. In the succeeding growth phase, a new hair is created which displaces the deceased one out of the follicle.
Several factors can interfere with hair growth cycles, such as disorders related to hormones or the immune system, pregnancy, negative drug reactions, and exposure to radiotherapy.