How Hair Grows, And Where It Goes

Chances are, at some time in your life, you’ve been envious of somebody’s hair—long, silky locks cascading across shoulders in gentle waves.

Or maybe you’ve wanted enough hair to stick up in a messy bun that looks carefree and glamorous at the same time.

If you have short hair, maybe you dream of thick, soft, finger-tempting layers your favorite person can’t resist caressing.

Your hair features your face and tells others a bit about you.

Like it or not, people make snap judgments about your personality, habits, gender, and health based on the length, style, color, and bounce of your hair.

Hair has two distinct structures:

The hair you see protruding from someone’s scalp is its dead cells pushed out by protein cells growing deep within each hair follicle (1).

The follicle is a tunnel from the epidermis (outer layer of skin) that ends with a pocket deep inside the dermis (2).

Hair cells begin their life and die in this pocket, so the part you see sticking out of your head doesn’t hurt when it’s cut.

You have about 100,000 follicles in your scalp.

The baby bulb (root) of the hair is made of protein cells at the base of the follicle that build a shaft.

Nearby capillaries nourish the bulb as cells divide (3).

Adequate circulation is needed to provide plenty of blood and nutrients to the growing cells.

Massaging your scalp promotes circulation and stimulates hair growth (4).

The blood delivers hormones that signal hair growth and structure throughout life.

Hair bulb cells divide every 23 to 72 hours, much faster than any other cell in the body (5).

Inner and outer sheaths surround the follicles to protect and form a growing hair strand.

The shape of your hair follicle determines whether your hair is straight, wavy, or curly (6).

The inner sheath ends below the opening of a sebaceous (oil) gland, and the outer sheath continues all the way to the gland.

Scent and sweat glands are also nearby (7).

Small, fan-shaped muscles called arrector pili or pilomotor muscles attach below the base of each hair that contracts when the body surface is chilled (8).

Contraction makes the hair stand up, causing “goosebumps” to appear, and the sebaceous glands secrete oil, or sebum, to condition the hair and skin (9).

Specific cells in the hair bulb, called melanocytes, make the pigment called melanin, determined by your genes (10).

Two types of melanin, eumelanin and pheomelanin, and their amounts create the color of each strand.

Hair has three layers, the inner medulla, middle cortex, and outer cuticle.

Most of the body of a hair shaft is the cortex.

The cuticle tightly wraps around the cortex in overlapping layers.

When hair gets damaged, dry, or frizzy, these layers “catch” on each other and snag other strands, the opposite of a silky, manageable mane where strands glide smoothly across each other.

The medulla consists of a soft, thin core of transparent cells and air spaces and only extends partway down the hair shaft.

Its length helps determine the thickness of your hair (12).

If the medulla doesn’t extend very far or is absent altogether, hair strands are thinner than those with medullae continuing further down the shaft.

Scalp hair typically grows about six inches per year.

We lose hair randomly, and at any moment, some of your strands will be in one of four stages of growth and shedding: anagen, catagen, telogen, and exogen.

Your hair’s density decreases as you grow from a baby to a grown-up because your body gets bigger, and there’s more distance between follicles.

With puberty, your body makes more sebum, but then as you age, the production of oil decreases.

And women typically have far less sebum than men at any age (18).

If you have trouble growing your hair past a certain length, it’s probably partly due to a shorter anagen (growing) phase.

It’s a wide range, and you might have a two-year anagen versus another’s seven-year phase.

Damage can also limit the overall length you can expect.

Hair on the rest of your body doesn’t grow very long because eyebrows, eyelashes, armpit, and leg hair all have short active growth phases, between only thirty to forty days (19).

Not everyone regrets losing hair. It’s a normal part of life, and sometimes it’s super sexy.

After hair loss, it may grow curlier or a lighter color.

If losing hair is uncomfortable for you in any way, consult your doctor.