Hair is constantly going through cycles of growth, resting, shedding. When hairs that are lost are not replaced, or when more hair follicles go into the resting phase, hair loss becomes noticeable. While there is ongoing debate regarding hair loss reasons, the list below shows many of the common contributing factors:



Ageing

The period for hair loss is between the 20 and 50 years of age. Some individuals arrive at the advance stages of hair loss sooner than others although it becomes increasingly evident as people advance in age.

Cosmetic Chemicals

Particularly bleaching, permanents, coloring.

Drugs/Medications/Radiation

Included are anticoagulants, antidepressants, contraceptive pills, amphetamines, some arthritis medications, some antibiotics, some blood thinners, medicines for gout, drugs derived from vitamin-A, certain drugs for ulcers, beta blocker drugs for high blood pressure. Cancer treatments such as chemotherapy and radiation therapy halt the growth phase of hair follicles which results in a sudden hair loss as those follicles all shed their hair at about the same time.

Heredity

Androgenetic alopecia is the term used to describe a genetic predisposition in men and women for pattern baldness or pattern hair loss. Although there is a dominant tendency for male pattern baldness, female members of a family can be transmitters as well.

Hormonal Imbalance

If the male and female hormones, androgens and estrogens, are out of balance, hair loss may result. Also an overactive or underactive thyroid gland can contribute to hair loss.

Illness and Severe Infections

These can include scalp fungal infections, Thyroid disorders, Hyperthyroidism, Hypothyroidism, Diabetes, Lupus.

Immune System Disorder

Alopecia areata is an immune system disorder which causes hair follicles to stop producing hairs. Advanced forms of the disorder are identified by the terms alopecia totalis when all head hair disappears, and alopecia universalis which results in all body hair disappearing.

Menopause

Due to hormonal changes after menopause, some women find their hair begins to thin. There are a variety of treatments available involving hormone replacement therapy (HRT). There may be side effects in some cases and experimentation may be necessary under the guidance of a physician.

Poor Blood Circulation

Poor blood flow to the scalp, insufficient nutrients in the blood, or poor drainage of waste products through the lymphatic systems can all contribute.

Pregnancy

Three to six months after delivering a child, many women notice a degree of hair loss as the hair goes into a resting phase because of the physiological impact of the pregnancy on the body.

Pulling

Traction Alopecia is the term used to describe loss of hair from constant pulling, as with tightly braided hair styles such as pony tails. Also the improper use of curling tongs or rollers can tug the hair so it weakens.

Sebum Buildup

Sebum buildup in the follicles attacks the hair bulb, the rounded area at the end of a hair strand which is rooted in the follicle. Sebum causes the hair bulb to shrink so the hair is not as well rooted. After the hair falls out the new hair strand growing in that follicle is weaker and thinner and the process is repeated until the hair follicle is so damaged it dies. (Sebum is a fatty substance secreted from the sebaceous glands most of which open into hair follicles.)

Stress and Nervous Disorders

Telogen Effluvium is the term used for a slowing down of new hair growth because of sudden or severe stress. The stress triggers a large number of hair follicles to enter the resting stage, so a few months after the stressful event, those follicles shed hair at about the same time.