The observable part of each head hair above the skin surface is known as the hair shaft. It is composed of a material called keratin, made up entirely of dead protein. The living part of each hair is situated below the skin surface in a small cavity known as a hair follicle.

There are three basic types of head hair. The first, lanugo hair, is to be found only on a human foetus, and is replaced Hair Point before birth by the second type, the very fine vellus hair. This is replaced in turn by the third and final stage, terminal hair, which is the mature hair shaft. During puberty the vellus hair covering of other bodily areas, such as in the pubic regions, also change into terminal hair.

Though terminal hair is the final stage head hair reaches, it should be noted that most of our body hair remains in the vellus stage. To give an example; the very fine 'down' barely discernible on a woman's face that softens her features.

The normal growth cycle of head hair consists of a number of stages. The period of active growth during which a hair may continue growing from between two to seven or so years is the anagen stage. The anagen I stage produces downy hair of the vellus kind. During the anagen 2 stage, the hair continues to grow to maturity, in other words it develops into the coarser appearing terminal growth. The length of hair that a person may achieve is directly related to the length of activity of the anagen stage.

After the anagen stage, the root of the hair becomes detached from the follicle, thereby curtailing any further growth. The follicle itself contracts during this period. This is known as the catagen phase, and will last for two weeks or so.

The hair finally enters the telogen, or resting phase. This lasts for a period of about four months, after which the follicle returns to its normal size and a new hair starts to form. The original mature hair may have already fallen out, but if it is still held in place the growth of the new hair will force it out. This process is continuous, and each hair follicle will be at a slightly different stage of this cycle, therefore gradual but continual shedding of hair will occur.

It is quite normal for between 10% to 20% of head hair follicles to be in the resting stage at any one time. Therefore even on an entirely healthy scalp of hair, up to 20% of potential hair cover may be missing. Normal hair loss due to these phases will result in a hundred or so scalp hairs being shed daily, slightly more during the autumn months, and less during the spring. The 'rate' of hair growth is also seasonal, and growth is faster during the spring and summer. Ultra violet radiation stimulates cell division, therefore exposure to an ultra violet sunlamp or natural sunlight will encourage hair growth. The rate of hair growth is also dependant on age. Men between the ages of 15 to 25 will experience the greatest rate of growth. As a man becomes older the rate of growth will gradually diminish, and hair growth will be very much slower after the age of 50.

It should also be realised that the actual number of follicles on a human scalp will vary in number according to the hair colour. Blondes have, the thickest hair at approximately 120,000 follicles. Brunettes have 100,000 or so, and Redheads have the fewest at around 80,000. Hair colour can therefore effect how quickly the onset of hair loss may become noticeable on an individual.

Returning to the natural cycle of hair growth for a moment, if for any reason a follicle does not leave the telogen stage and cycle through to the normal anagen stage it will produce no further hair, in other words baldness will result. If the follicle should enter the anagen I stage but progress no further, vellus hair may form but will not progress into mature terminal hair. In practical terms what may happen is that in an individual experiencing hair loss there is a gradual reduction in the 'vigour' of the hair, and before shedding permanently it may well have gone through a number of full cycles of growth, but each cycle will produce finer and less healthy hair shafts. Eventually, the cycle is arrested and only vellus hair will form. Usually this is a slow process over quite a substantial time period, though in some cases hair loss can be more dramatic. Either way, the hair eventually recedes in the familiar pattern of male baldness, leaving areas of total hair loss. However, if the balding areas are examined carefully very short and fine vellus hairs can be seen, but as the natural cycle has been arrested, the vellus hairs never mature into terminal hair.