Human Hair Growth
Going Straight to the Roots - Hair Structure, Hair Growth and Hair Loss
Say the words "human hair growth" and most of us instantly think of the stuff on top of our heads. Now, this is understandable enough. Human hair does tend to grow longer, thicker, and more plentifully on the scalp than elsewhere on the body. But the not-so-bald truth is that hair covers nearly every square inch of our face and body, no less thoroughly than if we were a chimpanzee or a gorilla.
In fact, you'll find only a few truly hairless regions on the skin's surface. These areas include the palms of the hand, the soles of the feet, the fingertips, the eyeballs, and the inside of the mouth.
Vellus Hairs ~ Human Hair Growth
The reason we appear less hairy than our close evolutionary relatives can be explained by hair types and how different types of hair are dispersed over the surface of the skin. In contrast to the body of a chimp, much of the human anatomy is covered by el1us hairs, which are remarkably short, fine, and colorless, rendering them in many locations all but invisible to the naked eye. Thus certain areas that seem to be hairless, such as the earlobes or the inside of the forearms, are actually coated by literally thousands of soft, downy vellus strands. In a word: hair!
Terminal Hairs ~ Human Hair Growth
The hairs that you comb are examples of terminal hairs. Terminal hairs can be found on the scalp, face, armpits, eyelids (in the form of eyelashes), eyebrows, legs, and pubic regions.
They are longer, thicker, and coarser than vellus hairs, and also contain melanin, which accounts for their coloring. Among terminal hairs, strands located on the scalp grow out more fully than strands covering, say, the extremities or the eyebrows, and even separate strands in the same general area will show variations in length, thickness, and curl. These variations are usually minor, but not always, which is why the hair strands on one portion of your head may "do the wave," while their neighbours lay quietly along the scalp.
A Single Strand of Hair
The visible portion of a hair strand, whether vellus or terminal, is not alive in the sense that the shampoo and conditioner ads would have you believe. Thus it cannot be "nourished," "rejuvenated," "invigorated," or made to thrive the way, for instance, a Plant thrives in response to watering or fertilization.
This is also because the living, reproductive portion of an individual hair strand resides deep below the skin's surface in a bulb like sac called a follicle. The part you see—and care for—is the hair shaft, which is composed of a non-living, fibrous protein known as keratin. Live cells within the hair root generate the shaft and sustain its subsequent growth.
The shaft itself is a two-piece affair, consisting of an outer, protective covering called the cuticle, and an inner, supportive nucleus called the cortex. In very basic terms, the cortex gives the hair strand its Structure and strength, while the cuticle shields the cortex from the environment.
When damage to the cuticle exposes the cortex to the elements, the affected hair becomes split or fractured. Too much washing, too much blow-drying, and overuse of the strong chemicals found in permanent wave solutions, straighteners, and other hair-care products are just a few of the most common causes of dry, brittle hair that wants to fray and break and hampers natural human hair growth.
Human Hair Growth
Updated July 1, 2011
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