Dihydrotestorone (DHT) Build builds up around the papilla, in effect, choking it. Each hair that is cycled  through the follicle becomes thinner and thinner until the follicle eventually shuts down and no longer produces thick hair.

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How Hair Grows

The portion of the hair that we can see is called the shaft. Each shaft of hair protrudes from its follicle, which is a tube-like pouch just below the surface of the skin. The hair is attached to the base of the follicle by the hair root, which is where the hair actually grows and where it is nourished by blood capillaries. Like the rest of the body, hairs are made of cells. As new cells form at its root, the hair is gradually pushed further and further out of the follicle. The cells at the base of each hair are close to the blood capillaries, and are living.

As they get pushed further away from the base of the follicle they no longer have any nourishment, and so they die. As they die, they are transformed into a hard protein called keratin. So, each hair we see above the skin is dead protein. It is the follicle, which lies deep in the skin, that is essential in growing hair. Also, the thickness of each hair depends on the size of the follicle from which it is growing.
 

Hair growth is not a continuous process: it has several stages.
 

• ANAGEN PHASE. The first phase is the growing stage. Hair grows at about 1 cm each month, and this phase lasts for anything between 2 and 5 years.

• CATAGEN PHASE. As this phase begins the bulb detaches from the blood supply and the hair shaft is pushed up.

• THE TELOGEN PHASE. This is followed by a resting stage, during which there is no growth. This phase lasts about 5 months.

• At the end of the resting phase, the hair is shed, and the follicle starts to grow a new one.

• At any moment, about 90% of the hair follicles of the scalp are growing hairs in the first phase; only about 10% are in the resting phase.

• If a follicle is destroyed for any reason, no new hair will grow from it.

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How baldness occurs

If any of the stages of hair growth are disrupted, the individual may become bald. For example, if follicles shut down (meaning that they stay in the resting phase, and then shed the hair) instead of growing new hairs, there will be less hair on the head. Another reason might be interference with the formation of new hair cells at the root during the growing phase. If follicles have been destroyed (ie., a burn, loss of layered skin or trauma), there will be baldness in that area. An individual can also look bald if the hairs are growing but are so fragile that they break just as they emerge from the follicle.

Recently, scientists at Columbia University in New York announced the discovery of a gene that appears to be the 'master switch' for hair growth. They found the gene after comparing the genes of hairless mice belonging to a mutant breed, and comparing the genes of 11 members of a family who had lost all their hair. This discovery is a step towards understanding how the hair follicle works and how baldness happens, and may lead to effective treatments becoming available in the future.

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How to know if you are losing too much hair - The Tug Test.

Bald areas are an obvious sign, but it can be difficult to tell whatever your hair is getting thinner. Hold small bunch of hair - about 15 or 20 - between the thumb and index finger. Pull slowly and firmly. If more than six come out there may be a problem.

Male & Female Pattern Baldness
 

NORWOOD Classification of Hair Loss Stages

Knowing that each case of hair loss is unique, Invision has made available several options to help both men and women with their thinning hair.

Receding hair is loss of hair at the sides of the forehead. It happens to most men eventually - usually at or after middle age, but it can start at any time after puberty. Some men also have loss of hair on top of the head, and eventually only the sides and back of the head have hair, forming a horseshoe shape. This is known as common baldness, Androgenic alopecia or male-pattern baldness.

Surprisingly, if you were to view a balding scalp under a microscope you would see that there are the same number of hair follicles as before, but each is shrunken, producing hairs that are fine, short and pale. You would also note that a higher proportion than usual of the follicles are in the resting phase. Three factors are at work in male-pattern baldness: male hormones, genetics and ageing.

Female Pattern Baldness: For women, thinning hair can occur throughout the entire scalp or in random patterns. In many cases hormonal changes and age will cause thinning over the entire scalp while certain genetic conditions and medical treatments can result in spotty or total hair loss. For these cases, Invision may incorporate several technologies to achieve a desired result.

The main hormone is testosterone. Both men and women have testosterone in the blood, but men have higher levels. The skin of the scalp converts testosterone to another substance called dihydrotestosterone (DHT). Hair follicles in areas that are destined to become bald seem to be especially sensitive to DHT, and shrink when exposed to it. Follicles on the sides and back of the head are not affected by DHT.

Confusingly, DHT is necessary for growth of the beard and hair on the chest. This explains why bald men can have bushy beards and hairy chests. Nobody knows how DHT produces opposite effects on hair growth on different parts of the body.

Heredity (genetics) is important. If you have relatives with thin hair or who are bald, you may well develop the same problem. This tendency can be inherited from either the mother's or the father's side of the family and can skip generations.

Ageing makes baldness more likely. Forty percent of men have noticeable hair loss by age 35, and 65% by age 60. Most elderly people have thin, fine hair even if they are not noticeably bald.