Hair grows in recurring cycles, with each cycle composed of three phases - anagen, catagen and telogen. The anagen phase is also referred to as the growth phase. About 85 to 90% of all the hairs in our heads are in this phase at one time. This part of the growth cycle lasts from 2 to 6 years and can continue for up to 8 years.



Once the hair reaches its maximum length in the anagen phase, the catagen phase of the growth cycle begins. This is a short phase, lasting only about 1 to 2 weeks. The catagen phase is also referred to as the transitional phase, when the cycle reaches the regressive stage and hair growth slows down. The follicle shrinks in size and the base begins to break down.

The telogen phase of the growth cycle is also known as the resting phase, when growth stops completely. This is the part where the follicle becomes degraded. This cycle lasts for about 6 weeks. Some hair may fall out but some stay in the follicle. Near the end of the telogen phase, new hair begins to form and grow. If the old hair is still attached, it is forced out and falls off the head. About 10% of our hair are in the telogen phase.

Hair growth cycle and hair loss

To understand hair loss, it is important that we know the nature of the cycle of hair growth. It is normal for people to lose 50 to 100 hairs a day. When this happens, you are probably in the telogen phase. You'll probably find these lost strands in your brush, comb or on your shower floor. This is normal and there is no need to worry because they will be replaced by new growth.

It is only when you're losing more and are noticing rapid thinning that you should be concerned. These are signs that your hair growth is not fast enough to replace lost strands and there is a possibility that your normal hair cycle has been disrupted.

Hair grows from the follicles which are found in the top layer (epidermis) of the skin. It is made of keratin, a form of protein, the same component of the epidermis, fingernails and toe nails. At the base of the follicles, a papilla is found, which is made of blood vessels and nerves. These ensure that the growth cycle runs uninterrupted.

Factors that can affect hair growth

Barring any obstacle, the hair growth cycle will continue unabated. It is only when some factors are applied that the cycle is disrupted or stopped. These factors can lead to temporary hair loss. Or if not, they can cause alopecia, which is more permanent. These can include hormones, nutritional deficiencies, diseases of the thyroid gland, chemotherapy and radiation. The cycle may also be affected by skin diseases of the scalp, trauma or stress.

Certain drugs can also disrupt normal growth, including anti-depressants, hypertension drugs, retinoids and birth control pills. The birth of a baby may also contribute to hair loss, along with diseases such as lupus, diabetes and HIV/AIDS. Men and women with eating disorders or undergoing severe dieting are also susceptible to this condition.

It is interesting to note that hair growth is not indicated in the human embryo in its initial stages. Hair growth only becomes apparent when hair follicles begin to appear in the early stages of the embryo's development, before it assumes a human form in the mother's womb. Evidence of hair growth begins to appear when the fetus is approximately 9 weeks old. By 9 months, the human fetus already has every hair follicle he/she will ever have.