Hair Growth: It’s Just a Phase

Hair growth patterns change across our bodies, throughout our lives, and from species to species. Check out Groupon's guide to explore the science behind the strands.

Hair varies in thickness and length across our body, from the head's massive jungle to the knuckles' tiny brambles. But regardless of where it is, each strand of hair cycles through three phases: anagen, also known as the active growth phase; catagen, or transitional phase; and telogen, or resting phase. During the growth phase, a new hair shaft sprouts from a follicle as its cells rapidly divide and grow upward, forming tightly packed bundles rich with keratin protein. Next, the transition phase kicks in for about two to three weeks, during which growth stops and the outer root sheath shrinks, anchoring the hair to the follicle as it enters the final phase. At that point, the follicle lies dormant until the hair is shed and the cycle begins again.

Not all hair grows at the same rate. On the scalp, hair grows about 6 inches per year, with each strand spending about two to six years in the active phase. Meanwhile, hair on the arms, legs, eyelids, and eyebrows actively grows for a much shorter period—only about 30–45 days—and spends more time in the resting phase, which is why waxing these areas helps curb unwanted hair growth. Humans need removal methods such as waxing because we don't shed our hair all at once like other mammals; our hair-growth cycles are random and staggered, whereas other animals' cycles are mostly synchronized.