Heredity or genetic influences on the hair follicle are the most common causes of hair loss in both men and women. While genes passed down to you from your parents play a big role in hair loss they are not, in and of themselves, guaranteed to make you lose your hair. Obviously, if most of the people in your family, whether on your mother’s or father’s side, are losing hair, then you have an increased chance of also losing hair. That said, some scientific evidence suggest that about 20 percent of people exhibiting genetic hair loss don’t have any known family members with the condition.

Besides the uncertainty of which hair loss genes you are going to receive from your family, the type of hair loss is also important when discussing hereditary influences. Male pattern alopecia and female pattern hair loss are the most common hair loss conditions connected with heredity factors, however, certain other hair loss conditions, such as alopecia areata may also be caused, in part, from genetic influences

The health of your hair is a barometer of your overall health, meaning that there are many health factors that can influence your hair cycle. For example, surgery requiring anesthesia can disrupt the hair cycle as can a high fever, in particular, a temperature greater than 101 degrees Fahrenheit.

In addition, numerous other general health factors can be important. Lupus (an autoimmune disease), digestive problems and infections may be relevant to your condition, causing conditions such as telogen effluvium (hair shedding) or cicatricial alopecia (scarring hair loss). The most important health influences are often the ones that occurred approximately four to sixteen weeks before the hair loss even became noticeable.

Published research has shown that your hair needs a plentiful supply of protein, energy-producing molecules (glucose) and certain vitamins and minerals for optimal growth to occur. As the hair follicle is a nonessential tissue and, therefore, one of the last tissues to receive nutritional substances (or one of the first to have them reduced), any long-term deficiencies may lead to hair loss.

Protein deficiency can be a frequent cause of hair loss, because protein helps the body build hair fibers, which consist of 80 to 95 percent protein (this is especially relevant for vegetarians). For those who eat infrequently, the amount of energy available at your hair growth site may be deficient, causing the fair to fall out prematurely. The most common nutritionally related hair loss occurs while dieting. Severe weight loss due to dieting can often cause a temporary increase in hair shedding (telogen effluvium) due to metabolic changes in the body.

Taking certain medications can cause hair loss in some people while the same medicine may not cause hair loss in others. Stopping a certain medication can also cause hair loss in some, but not in others. In addition, certain medications can cause hair loss the first time they are taken, but not subsequent times (once the body adjusts to the medicine, the hair loss stops), or they don’t cause hair loss the first time but do subsequent times (possibly due to the medicine accumulating in the body).

It’s difficult to categorically say that one particular medicine causes hair loss and another doesn’t, as medicines can react differently in different people. However, some of the medications most commonly reported to cause hair loss are: chemotherapy medications, antidepressants, thyroid medicines, oral contraceptive pills and cholesterol medicines. The hair loss condition often caused by medications is called telogen effluvium (hair shedding).

Hormones control hair growth to a large extent and there are many hormonal irregularities that can affect the hair cycle. Often these produce other symptoms that can indicate their presence, although even if there is an absence of any other symptom, it does not rule out that a hormonal factor is present. Men using anabolic steroids (either for medical or recreational purposes) may experience increased hair loss. For women, hormonal influences on their hair may be indicated by irregular menstrual cycles, polycystic ovarian syndrome, menopause and post-partum. Hormonal problems can contribute to certain hair loss conditions, in particular, heredity hair loss and telogen effluvium (hair shedding).

Although not technically hair loss from the scalp, losing hair through breakage (traction alopecia) can cause hair thinning and slow growth. Breakage can occur due to chemical over-processing and/or incorrect styling, drying or brushing techniques. For example, using a dryer that is too hot can cause the hair to burn, often so much so that you can smell it burning as you dry. Vigorous brushing can also cause the hair to break.