Understanding how hair grows helps we understand how to remain hair from growing. Each hair is enclosed in a pilosebaceous unit, which consists of a hair shaft, hair follicle, sebaceous gland, and erector pili muscle. Hair growth and shedding is a continuous cycle through 3 phases. The anagen phase is the growth phase, the catagen phase is a transitional state, and the telogen phase is the resting phase. Hairs spend a changeable amount of time in each phase determined by genetics, hormones, and region of the body. Hair in the anagen phase is more vulnerable to injury than hair in the telogen phase. All of these factors must be considered when deciding a method of hair removal.