Our hair is more complex than meets the eye and plays a major role in the appearance of men and women. Hair creates gender identification and transmits sensory information to the brain. We develop all our hair follicles by the 22nd week of gestation when about 5 million of them, with 1 million of the scalp, are created. We do not generate new hair follicles after that.
We have hair everywhere on our bodies, except on the mucous membranes and glabrous skin at the palm of our hands, the bottom of our feet and our lips. Some of the hair is visible, some not so much, but each and every follicle is working on its own schedule. Hair grows all the time and dies all the time, an intricate system that makes sure our hair doesn’t grow in batches but uniformly all around. What is really the science behind our hair, and what makes it grow? The hair has 2 distinctive parts: the follicle which is imbedded in the skin and the shaft which is visible above the skin.
The follicle The follicle is part of the epidermis and extends all the way down to the dermis. The base of the follicle is called Papilla and contains blood vessels that nourish the cells. The living part of the hair is at the very bottom and is called a bulb. Cells of the bulb divide every 23-72 hours, faster than any cell in the body, and push the hair to the surface. The follicle is surrounded by two layers, or sheaths, one of them follows the hair shaft and ends under the oil glands and sometimes scent glands (in animals). A muscle is attached to the layer underneath and when it contracts, as in fear and rush of adrenaline, it causes the hair to stand up. The familiar phrase “Make the hair on my neck stand up” is physically true.
The hair The hair is made of keratin, type of hard protein and consists of three layers; the medulla, the cortex, and the cuticle. The cuticle is made of an almost see-through and tightly formed structure that looks like overlapping fish scales, or roof shingles. The two inner layers hold the pigment that gives the hair its color while the cuticle is the protective layer. The main dilemma of hair color and hair straightening manufacturers is how to chemically open those scales to let the color pigment and hair straightening treatments in, without damaging the hair‘s keratin.
The average growth of a hair is about 6 inches per year and is not seasonal, unlike other mammals. It is random, and at any time we have hair that is in one of three stages: growth, transition and shedding.
The growth stage
(Anagen) is the most active one. A new hair is formed and it starts to push the old hair up the follicle and out. The longer the active phase continues, the longer the growth period is. Healthy hair continues to grow for 2 – 6 years. Some people say they’ve reached a stage where their hair is not getting any longer. They have probably reached the maximum of the growth period that their follicle condition allows.
When the hair is in its growing stage, under the skin, it is the only time the hair is a living thing. What we see on our scalps is considered to be “dead” keratin.
The second stage (Catagen) is the transition. The hair is not growing anymore and the outer sheath shrinks around the root of the hair. The follicle is renewing itself by shrinking to about 1/6 of its original size, cutting the blood supply to the hair.
The third stage (Telogen) is the resting stage, which leads to shedding. It lasts about 100 days for the hairs on the scalp, and longer for hair on eyebrows, arms and legs, before the hair strand is pushed up and out by the new. We normally shed about 25 -100 hairs a day.
What many keratin hair treatments aim to do is ‘plug in’ the holes in the cuticle of the hair to make it smooth and shiny. For after all what is keratin , but what our hair, dead or alive, is made of?