Normal Hair Growth Patterns
The normal hair growth cycles last between two to six years. On average, each hair grows about one centimeter (less than half an inch) per month during its growing phase.

About 90 percent of the hair on your scalp is growing at any one time. The other 10 percent is in a resting phase. After two to three months, resting hair begins to fall out and new hair will start to grow in its place.

It is normal to shed some hair each day as part of this cycle. However, some, men, women and children can experience excessive hair loss.

Excessive Hair Loss
Different kinds of things can cause excessive hair loss

Hair loss can be related to the stress of illness or after surgery and is usually temporary.

Hormonal problems can also cause hair loss. An overactive or underactive thryoid can also cause your hair to fall out.

Hair loss can occur if male or female hormones, known as androgens and estrogens, are out of balance.

Medicines can also cause hair loss, and is usually resolved once medications are stopped.

Certain infections can cause hair loss. such as fungal infections of the scalp, and are treatable.

Hair loss may also occur as part of an underlying disease.