This simple reference (all beginning with the letter 'H' for Hair) is not exhaustive, but covers many of the common causes of hair loss (alopecia) for both men and women. An individual's hair loss may be caused by one or more of these factors. Some of these influences on the hair cycle may cause permanent hair loss whilst others only temporary.

1) HEREDITY: many hair problems are passed down in the genes. If one or both parents have hair loss or thin hair, then the chances are increased that their children will also suffer the condition. The more family members that have genetic hair loss, the higher the percentage chance there is for an individual to also suffer the condition.

2) HORMONES: genetic hair loss in both men and women tends to occur when androgens (male hormones) act upon the hair follicle producing a reduction in the size of the affected follicles, which results in a reduction in the diameter and length of the hairs that they produce. A low functioning thyroid (hypothyroidism) or other endocrine gland malfunction can also cause hair loss and hair thinning in men and women. For some women, other hormonal factors such as; irregular menstruation, taking the contraceptive pill, giving birth, or going through menopause can also affect the hair cycle leading to thinner hair.

3) HEALTH: many illnesses can cause the hair to fall out, particularly if associated with a high temperature or an operation that has needed general anaesthetic. Also, certain autoimmune diseases such as lupus can affect the hair cycle and/or hair follicle.

4) HEALING (medication): certain medications or treatments for a particular illness can cause the hair to fall out. Radiation therapy, chemotherapy, anticoagulants, lithium based medications, large doses of vitamin A, and agents that block cholesterol synthesis can all inhibit hair growth.

5) HASSLE (stress): stress is a very common trigger for hair loss. Many researchers believe that stress can aggravate the condition as the skin becomes more sensitive to the effects of androgens (male hormones) during stressful episodes. Severe stress can also influence diffuse shedding of hair (telogen effluvium). Alopecia areata or "patchy" hair loss has also been connected to stress episodes as has trichotillomania (hair pulling).

6) HUNGER (diet): it is commonly accepted that undernourishment slows the growth rate of hair. This is because basic amino acids, fats and vitamins are all necessary to grow healthy hair. Some recent research studies have shown that deficiencies in iron stores, vitamin B-12, & folic acid levels can also lead to an increase in hair shedding. Certain excesses of some vitamins, particularly the fat soluble ones, can also cause temporary hair loss as can severe weight loss due to dieting or inadequate intake of proteins.

7) HAIRDRESSING: over processed hair can become very brittle leading to severe breakage. Also, vigorous brushing or blow drying with very hot air can cause the hair to come out or to break (traction alopecia).