Zooming in on Hair Follicles

We’re constantly busy with our bodily hair, but there’s far more to it than what appears on the surface. Hair plays a key role in the appearance and confidence of both men and women, helps transmit sensory information, and creates gender identification. Here are some answers to questions you may have.

Biology 101
Believe it or not, by its 22nd week, a developing fetus has all of its bodily hair follicles formed — about 5 million of them. Of those, 1 million follicles are on the head and 100,000 of those reside on the scalp. Sadly, that’s the most follicles we’ll ever have, as humans don’t generate new hair follicles during the course of their lifetime. And yes, the density of our scalp hair gradually decreases as we age, but the reason is that our scalps expand as we grow!

Hair Structure
A hair follicle is a mammalian skin organ that produces hair. The shape of the actual hair follicle effects the shape and texture of each one’s hair. Hair also has two distinct structures — the follicle (within the skin) and the shaft (the part visible above the scalp). The follicle is on the epidermis, the surface layer of the skin that you can touch, and extends down into the dermis (inner layer). At the base of the follicle is the papilla, which contains tiny blood vessels that nourish the cells. The living part of the hair is the very bottom portion surrounding the papilla, called the bulb. The cells of the bulb divide every 23 to 72 hours, extraordinarily faster than any other cell in the body. However, the hair shaft which comprises three layers of a hard protein called keratin, is actually dead — yes it’s true — so the hair you see is not a living structure, pretty much like our nails.

Sebum & Aging
An inner and outer covering surrounds the follicle protecting and forming the growing hair shaft. The inner covering follows the hair shaft and ends below the opening of a sebaceous (oil) gland; the outer continues all the way up to the gland. The sebaceous gland is vital because it produces sebum, which conditions the hair and skin. If you have an oily skin and are prone to breakouts, you’ll often hear the word sebum. However, it also keeps the skin supple and wrinkle-free — while post-puberty our body produces loads more sebum, as we age we begin to make less. The bad news for the girls is that as they get older women have far less sebum production than men do and hence look older sooner.

How Long Does Hair Take to Grow?
Another question we’re always asking is how fast the hair on our scalp grows? Well, the average is about .3 to .4 mm/day or about 6 inches a year. Unlike other mammals, human hair growth and shedding is random and not seasonal or cyclical. At any given time, a arbitrary number of hairs will be in one of three stages of growth and shedding: anagen (active phase that lasts 2-6 years when the hair grows about 1cm every 28 days), catagen (a transitional stage in which 3% of all hairs are in at any time), and telogen (the short resting phase which usually accounts for 6% to 8% of all hairs). If you have difficulty growing your hair beyond a certain length it’s because they have a short active phase of growth. On the other hand, people with very long hair have a long active growth phase. Also, the hair on the arms, legs, eyelashes, and eyebrows have a very short active growth phase of about 30 to 45 days, explaining why they are so much shorter than scalp hair.

Hair Loss
At the end of the resting phase (telogen), the hair falls out (exogen) and a new hair starts growing in the follicle beginning the cycle again. Normally, about 40 (0–78 in men) hairs reach the end of their resting phase each day and fall out. When more than 100 hairs fall out daily, clinical hair loss (telogen effluvium/hair thinning) may occur. Also, a disruption of the growing phase can cause an abnormal loss of anagen hairs (anagen effluvium).

So, whether you cut it, grow it, dye it, wash it, pin it up, wear it loose, shave it, wax it, or laser it, you’re a mammal and your hair has a life and lifecycle of its own!