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The Structure of Hair

From cuticle to follicle to shaft, a deeper look inside your hair.

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Hair Structure

We don’t always treat our hair well. In fact, if your hair only knew what you were putting it through, it might be pulling its hair out! To show you, let’s check out the structure of hair—how it grows, how it can end up in your shower drain, how it can look as lively as sun-scorched grass.

The average head has 150,000 hair follicles. The adult body has five million. That number comes from your genes and remains constant throughout your life.

QUIZ: How Healthy is Your Hair?

The thickness and condition can change, and so can whether you lose the strands that come from these follicles. You lose 50 to 200 hundred hairs a day, on average. Individual hair strands grow about six inches per year. Women from 16 to 24 years old grow it the fastest.

Some people have trouble growing hair beyond a certain length due to a short active phase of growth. People with very long hair have a long active phase of growth.

Arms, legs and eyelashes have a shorter active phase of growth, about 30 to 45 days. That’s why hair in these areas is so much shorter than on your scalp. Eyelash transplants from the scalp need to be trimmed every few weeks. 

WATCH VIDEO: How Your Hair Grows

Remarkably, each hair strand has its own blood supply. As a result, your health and diet greatly influence your hair. Hormones also control your hair. That’s why men have beards, chest hair and male-pattern baldness, while women typically do not.

Your hair is made of a follicle and shaft. Follicles are tunnel-like segments in the epidermis of your skin. They live under the skin’s surface and extend into the dermis. The hair follicle base has few blood vessels to nourish the cells. The bulb at the base is the living part. The shaft that we see above the skin is dead.

The hair shaft’s made of keratin protein. The majority of the shaft is made up of the inner layer (medulla) and the middle layer (cortex). The hair cuticle, which looks like a tile roof under the microscope, serves as the outer, protective layer that covers the medulla and cortex.

Your hair needs oil to keep it shiny. Tiny muscles surround your hair, occasionally giving you goose bumps when you feel a shiver. These muscles squeeze glands that moisturize your hair with sebum—your personal vitamin E-rich hair and skin conditioner.

MORE: Good Housekeeping Finds the Best Anti-Aging Products for Your Hair

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