Have you ever stopped and really wondered why we have hair? These days of relative comfort, we don’t need our hair to keep us warm or protect us from the elements. It was not always thus! Human hair, much like the fur that covers animals, is a relic of evolution; an adaptation to protect our bodies.
On average, hair grows about 6 inches each year. Hair growth is a continuous cycle, some hairs in one stage of the cycle, other hairs in a different stage. Called anagen, catagen, and telogen, each stage is distinctive.
Anagen is the active stage of hair growth, when the hair itself grows by about 1 centimeter in a 28-day span. This occurs for about 3 to 6 years of activity. How long your hair stays in this phase is dependent on several factors, including your age, what you’re eating, your hormone levels, and more. At any given time, about 85% of your hair follicles are in this stage.
Interestingly enough, the duration of the anagen stage also determines the eventual length of the hair growth. Ever wonder why your eyebrows don’t just grow straight down your face like the hair on your scalp grows down your back? Shorter anagen stage means shorter hair!
The catagen stage follows anagen, and concludes the growth period of the active hair. During the catagen stage, the body is capable of producing new hairs. This is a transitory time, when growth turns to resting, and the cycle typically lasts several weeks, and even up to four.
During this time, cells cease growth and pigmentation, and the interior follicle shrinks down, among other complex processes.
The final stage is called the telogen phase, and typically about 8% of your hair is in this concluding stage at any one time. This is a time of inactivity of the hair, which can last anywhere from 2 to 4 months. Between 25 and 100 strands of hair are shed while in this phase during an average day. Once hairs are shed and the follicle exists the telogen phase, new hair will grow to replace those that were lost
Your hair is more complicated than you thought!
Knowledge of the cycle of hair growth gives you a valuable tool to understanding what is “normal” growth and hair loss. If you are losing more than the 25-100 hair strands in a day, it is definitely time to examine why that might be (if you have exceedingly thick hair, the higher end is going to be the norm; finer hair vice versa, of course). Pay attention to what’s “up” on your head!