The Biology Behind Hair Growth

The Biology Behind Hair Growth
Nothing in​ life is​ as​ simple as​ it​ seems,​ so it​ should come as​ no surprise that the​ strand of​ hair that you​ found on​ your brush this morning is​ an amazingly complex part of​ your body. Hair begins appearing on​ the​ human body while it​ is​ still in​ the​ womb. By the​ time a​ developing fetus reaches 22 weeks old,​ there are already 5 million follicles on​ the​ body. Interestingly enough,​ that is​ all of​ the​ follicles that will ever develop regardless of​ how long we​ live. None will ever be added.
Hair Anatomy
Hair consists of​ a​ follicle,​ which is​ embedded in​ the​ skin,​ and the​ shaft of​ hair which appears on​ our body. the​ follicle itself consists of​ multiple layers with each layer having a​ specific function. the​ papilla lies at​ the​ base of​ the​ follicle. Capillaries are connected to​ the​ papilla and they supply blood to​ the​ cells which surround the​ bottom part of​ the​ hair strand called the​ bulb.
Surrounding the​ follicle are two sheaths,​ inner and outer,​ which are designed to​ both protect the​ hair shaft from damage,​ and to​ help it​ grow out in​ the​ proper direction. the​ inner sheath runs next to​ the​ hair shaft and ends at​ the​ oil sebaceous gland. the​ outer sheath runs to​ the​ gland and ends at​ the​ erector pili muscle. This is​ the​ muscle that causes our hair to​ stand on​ end when it​ contracts.
The hair shaft is​ comprised of​ three layers of​ dead protein cells called keratin. the​ innermost layer,​ known as​ the​ medulla,​ is​ not always present in​ every hair shaft. the​ second layer,​ known as​ the​ cortex,​ provides the​ bulk of​ the​ hair shaft. the​ hair color is​ mostly determined by the​ pigmentation contained in​ this layer. the​ outermost layer is​ called the​ cuticle. it​ is​ comprised of​ a​ series of​ overlapping cells. the​ hairs luster and sheen comes from the​ cuticle.
How Hair Grows
Scalp hair grows at​ an average rate of​ six inches per year,​ or​ only . 3. 4 mm per day. There are three distinct stages of​ hair growth.
Catagen Phase
This transitional phase runs about two to​ three weeks. at​ any given time approximately 3% of​ your hair is​ in​ this phase. There is​ no hair growth during this period while the​ out portion of​ the​ hair root sheath shrinks and attaches itself to​ the​ root.
Telogen Phase
This phase,​ known as​ the​ resting period is​ experienced by approximately 15% of​ your hair. Telogen lasts for​ around 100 days for​ scalp hair and significantly longer for​ other body hair.
Anagen Phase
This phase defines a​ period of​ activity where the​ hair cells are dividing and new hair growth occurs. This phase can last for​ as​ long as​ two to​ six years. Shorter growth periods are indicative of​ people who have trouble growing their hair long.
Hair Growth Disorders
There are two hair growth disorders that affect humans. Hirsutism is​ a​ condition affecting mostly females. it​ is​ defined as​ a​ condition where excessive thick and dark hair growth is​ experienced in​ areas typically reserved for​ males. These areas include the​ face,​ chest and the​ areolae or​ area surrounding the​ nipple. Hypertrichosis is​ a​ condition which causes excessive hair growth in​ areas of​ the​ body where visible hair is​ not normally present. Both of​ these conditions are treatable.

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