Hair grows everywhere on the human skin except on the palms of our hands and the soles of our feet, but many hairs are so fine they're virtually invisible. Hair is made up of a protein called keratin that is produced in hair follicles in the outer layer of skin. As follicles produce new hair cells, old cells are being pushed out through the surface of the skin at the rate of about six inches a year. The hair you can see is actually a string of dead keratin cells. The average adult head has about 100,000 to 150,000 hairs and loses up to 100 of them a day; finding a few stray hairs on your hairbrush is not necessarily cause for alarm.
At any one time, about 90% of the hair on a person's scalp is growing. Each follicle has its own life cycle that can be influenced by age, disease, and a wide variety of other factors. This life cycle is divided into three phases:
- Anagen -- active hair growth that lasts between two to six years
- Catagen -- transitional hair growth that lasts two to three weeks
- Telogen -- resting phase that lasts about two to three months; at the end of the resting phase the hair is shed and a new hair replaces it and the growing cycle starts again.
WHAT ARE CAUSES FOR HAIR FALL?
Most people normally shed 50 to 100 hairs a day. This usually doesn't cause noticeable thinning of scalp hair because new hair is growing in at the same time. Hair loss occurs when this cycle of hair growth and shedding is disrupted or when the hair follicle is destroyed and replaced with scar tissue.
The exact cause of hair loss may not be fully understood, but it's usually related to one or more of the following factors:
- Family history (heredity)
- Hormonal changes
- Medical conditions
- Medications
- Patchy hair loss. This type of nonscarring hair loss is called alopecia areata (al-o-PEE-she-uh ar-e-A-tuh). It occurs when the body's immune system attacks hair follicles — causing sudden hair loss that leaves smooth, roundish bald patches on the skin.
- Scalp infections. Infections, such as ringworm, can invade the hair and skin of your scalp, leading to scaly patches and hair loss. Once infections are treated, hair generally grows back.
- Other skin disorders. Diseases that cause scarring alopecia may result in permanent loss at the scarred areas. These conditions include lichen planus, some types of lupus and sarcoidosis.
- Hair-pulling disorder. This condition, also called trichotillomania (trik-o-til-o-MAY-nee-uh), causes people to have an irresistible urge to pull out their hair, whether it's from the scalp, the eyebrows or other areas of the body.
- Radiation therapy to the head. The hair may not grow back the same as it was before.
- A trigger event. Many people experience a general thinning of hair several months after a physical or emotional shock. This type of hair loss is temporary. Examples of trigger events include sudden or excessive weight loss, a high fever, surgery, or a death in the family.
- Certain hairstyles and treatments. Excessive hairstyling or hairstyles that pull your hair tight, such as pigtails or cornrows, can cause traction alopecia. Hot oil hair treatments and permanents can cause inflammation of hair follicles that leads to hair loss. If scarring occurs, hair loss could be permanent.




