Excessive Hair Loss (more than 100 hairs a day) can be caused by inherited factors, disease, stress, medications, injury, aging, or hair care.

Inherited hair loss

The most common cause of hair loss is genetics - you inherit the tendency to lose hair from either or both of your parents. This is called male-pattern hair loss or female-pattern hair loss. The medical term for this type of hair loss is androgenetic alopecia. In this type of hair loss, your genes affect how your hair grows. They trigger a sensitivity to a class of hormones called androgens, including testosterone, which causes hair follicles to shrink. Shrinking follicles produce thinner hair and eventually none at all. Men generally develop bald spots on the forehead area or on the top of the head, while women have an overall thinning of the hair throughout the scalp. About half of all people have inherited hair loss by about 50 years of age.

Common causes of hair loss include:

• Ringworm of the scalp (tinea capitis), which is common in children.
• Mental stress or physical stress, such as recent surgery, illness, or high fever. You may have a lot of hair loss 4 weeks to 3 months after severe physical or emotional stress. Your hair usually will grow back within a few months.
• Hair care. Pulling your hair back too tightly or wearing tight braids or ponytails can cause hair loss. You may lose hair around the edge of the hairline, especially around the face and forehead. Using curling irons or dyes continually can also result in hair loss. Hair usually grows back when these activities are stopped.
• Age. As you age, your hairs tend to break more easily, and hair follicles do not grow as much hair.
• Poor nutrition, especially lack of in the diet. Hair returns after you change your diet to get enough of these nutrients.
• Thyroid diseases.

Some more causes include:

• Alopecia areata is an autoimmune disease in which your immune system attacks hair follicles which can result in obvious round hairless patches on any area of the scalp or body. Severe cases involve many bald patches of hair or complete loss of hair on the scalp or body, although in some cases there is hair thinning without distinct patches of baldness. Hair usually grows back within 1 year without treatment; however 10% of people with the condition may never regrow their hair.
• Side effects of medications or medical treatments such as blood thinners or chemotherapy. Hair usually grows back after you stop using the medication or when the treatment is over.
• Trichotillomania, a compulsive behavior in which a person pulls hair out of the scalp, eyelashes, or eyebrows. There is usually mounting tension before pulling and a feeling of relief afterward. Trichotillomania often results in noticeable hair loss.
• Injury to the scalp including scarring. Injuries can damage hair follicles and cause hair loss.
• Changes in hormone levels. Childbirth, taking birth control pills or changes in a woman's menstrual cycle can affect the hair growth cycle and cause hair loss. Hair usually will grow back.

Hair loss can be categorized by types. Different types of hair loss may have different causes. For example, one type of hair loss known as telogen effluvium is caused by stress and side effects of medication. Another hair loss type, traction alopecia is caused by chemical treatment of hair with dyes, bleaches, or straighteners.