why does hair fall?

Everyone loses some hair everyday but it can be frustrated when it change how you look. When should we concern that it is excessive hair loss?

The primary functions of human hair are body insulator, protection of skin from sun damage and trauma, prevention of foreign body from entering the eyes. Beauti cation is the secondary function of hair but it seems to be the primary importance for humans.

Understanding about hair growth cycle will give us a clear picture of causes of hair loss. Once the hair growth cycle starts, it should keep going and never stop. But, for those who are losing their scalp hair, it may be some defect in the hair cycle. Each hair passes through the phases independent of the neighboring hairs. Hair follicles grow in repeated cycles. One cycle can be broken down into three phases.

1) Anagen - growth phase

2) Catagen - transitional phase

3) Telogen - resting phase

Anagen Phase - growth phase

In a normal healthy individual, up to 85-90% of hair follicles are in the anagen phase. This is the active growth phase of hair follicle. During this stage the root of the hair is dividing rapidly. The longer the hair stays in the anagen phase, the longer it will grow. Scalp hair stays in this active phase for 2–6 years. The normal rate of hair growth is approximately 1 cm per month. At the end of the anagen phase an unknown signal causes the follicle to go into the catagen phase.

Catagen Phase - transitional phase

At the end of the anagen phase the hair enters into catagen phase, it is the end of hair growth. This phase lasts only about 2 - 3 weeks. The rst sign of catagen is the cessation of melanin production in the hair bulb follow by cut off blood supply to the hair follicle. The hair follicle shrinks and enters the telogen phase.

Telogen Phase - resting phase

Telogen phase is the phase following catagen phase and normally lasts about 2-3 months. About 10-15 % of hair follicles on the scalp are in this phase. During this time the hair does not grow but stays in a resting phase and attached to the follicle. At the end of telogen phase the hair falls out and is replaced by a new growing hair. If the percentage of hair follicles in telogen phase increases signi cantly then there will be an increase in hair shedding and diffuse thinning of scalp and/or body hair will occur which is called Telogen Ef uvium.

There are many potential causes of Telogen Ef uvium.

The common causes are listed below

1. Hormones

2. Fever-induced alopecia

3. Acute blood loss

4. Extreme physical stress such as surgery, systemic anesthesia

5. Drug and chemical induced Telogen Ef uvium