Excepting a few spots, the human body is completely covered with hair follicles. Most follicles are tiny, and many of the hairs they produce do not grow long enough to emerge out from the pore.

Hair is made from a protein called keratin. The only living part of the hair is the bulb, which is attached to the base of the follicle (a narrow pocket of skin). The follicle supplies oxygen and nutrients to the bulb and lubricates the hair shaft with an oily substance called sebum. At the base of the bulb are dermal papilla cells which are the specialised embryonic cells from which each new hair is born. The bulb is surrounded by blood vessels and adipose (fat) tissue.

Each hair goes through three phases of growth:

• The Anagen or active growth phase, lasts two to seven years. During this phase, the embryonic cells within the bulb continually drive the growth of the hair up the lubricated follicle.
• The next phase is the Catagen or transition phase – which lasts about two weeks. During this phase, the hair shaft moves upward toward the skin's surface, and the dermal papilla begins to separate from the follicle. This terminates the nourishment and growth of the hair. The final phase is the Telogen or resting phase.
• This lasts about three months and culminates in the shedding of the hair shaft.

Hair is in a constant cycle of growth, rest and renewal. On the scalp, there are approximately 100,000 hair follicles. Over the course of three years, every one of these follicles will produce a hair that grows, rests, falls out and then regrows. That means that every 1,000 days, you shed 100,000 hairs. This equates to 100 hairs shed every day.

As long as the new hair that grows from that follicle is the same as the one it replaces, the hair density will remain constant.

There are a range of types of hair loss (or alopecia), with the most common being Patterned hair loss.

Patterned Hair loss is the most common cause of hair loss in both men and women and is the result of genetic and hormonal factors. Patterned Hair loss is so common that it’s considered to be a normal part of the ageing process.

Patterned hair loss is caused by androgen hormones - produced in different amounts by both men and women - that affect the hair follicles in people with a genetic susceptibility. More specifically, it is a hormone called Dihydrotestosterone (DHT) which is a bi-product of the metabolism of testosterone by an enzyme called 5-alpha reductase.  This is where the term androgenic alopecia comes from.

DHT stimulates a process called “miniaturisation” which is characterised by shrinking of the hair follicles. As the follicles get smaller, the hair that can grow from each follicle also becomes shorter and finer than the hair it replaces. Eventually, the new hairs are so short and fine they become invisible and the scalp becomes bald. In this process, DHT triggers a wide range of biological mediators (cytokines and chemokines) to cause the dermal papilla cells under the hair follicle to decline which in turn commences a long term reduction of the anagen growth phase and eventual conversion of normal (terminal) hairs into smaller (vellus) hairs.

Patterned hair loss is different in Men and Women.

Male pattern baldness accounts for more than 95% of hair loss in men – thanks to naturally higher levels of testosterone. By age 35, two-thirds of men will have some degree of appreciable hair loss and by age 50 approximately 85% of men have significantly thinning hair. In men, hair loss usually begins above the temples, and the receding hairline eventually forms a characteristic "M" shape. Hair at the top of the head also thins, often progressing to baldness.

Hair loss in women produces scattered thinning over the top of the scalp (especially at the part line) rather than a bald spot. Patterned hair loss occurs in over 55% of women as they age. For most women, the hair loss is subtle, but about 20 per cent of women develop moderate or severe hair loss. Baldness is only seen in a minority of women (less than five per cent). Even though women have much lower levels of testosterone normally (and less DHT), fluctuation in hormones – caused by stress, medical conditions, menopause and pregnancy – can cause hair to grow more slowly and become much thinner.