Hair loss information and treatments

The Biology of Hair Loss

To understand how hair loss occurs, one must first understand how hair grows. Normal hair growth may be interrupted by age- or disease-related changes to body chemistry, or by changes in the external environment that cause similar biochemical alterations, such as dietary deficiencies, the effects of prescription and over-the-counter drugs.

The Hair Growth Cycle

Every hair on your body goes through three distinct stages of life:

At any given time, about 90% of the hairs on your head are in the growth stage; the other 10% remains in the resting stage. Normally, hair growth occurs at a rate of about one half of an inch per month, although this pace decreases as a person ages. Daily hair loss or “shedding” is normal, although hereditary and environmental factors can hasten this process.

Biochemical Changes in Androgenetic Alopecia

The name “androgenetic alopecia” is a tip-off – “androgenetic” means caused by androgens. An important biological feature of androgenetic alopecia ( AA ) is a change in the effect of the naturally occurring androgen or hormone, dihydrotestosterone ( DHT ). Normally, the enzyme 5alpha-reductase ( 5AR ) converts testosterone to DHT in the hair follicle.

Men and women genetically predisposed to pattern baldness often have higher levels of DHT in their scalp, and/or may be more sensitive to its effects. DHT acts on the hair follicle, causing it to undergo a shortened anagen or “growing” phase. The hair shaft becomes progressively shorter, finer and lighter in appearance until it is virtually transparent and does not emerge from the follicle, a process known as “miniaturization.”

Propecia ( finasteride ) acts by inhibiting 5AR, thus minimizing the amount of DHT formed.

Interestingly, not all hairs on the scalp are equally affected by AA, particularly in men. While women with AA experience generalized hair thinning over the scalp, men exhibit a pattern baldness characterized by hair loss on the front of the scalp and the crown, with hair often remaining on the sides and back of the head. These remaining hairs appear to be more resistant to the effects of DHT and are therefore used in hair transplant surgery.

Nutritional Deficiencies

Each hair is nourished by a blood vessel near the base of the follicle. Although nutritional deficiency alone rarely causes hair loss, in people with iron deficiency ( anemia ) or protein deficiency, the hair may not receive sufficient nutrition to form the emerging hair properly during all or part of the growth phase. In people with anorexia, many hair follicles may “shut down” their growth phase to minimize energy output ( a form of telogen effluvium ).

Effects of Ingesting Drugs

Hair loss caused by taking prescription or over-the-counter drugs resembles hair loss in telogen effluvium, /effluviums.htm and is therefore termed “drug-induced telogen effluvium.”

Chemotherapy drugs interrupt the natural cellular growth cycle by a variety of biochemical mechanisms. Consequently, cell division is virtually halted in the digestive tract, bone marrow and hair follicles, where cells normally divide rapidly. Fortunately, hair loss caused by anti-cancer drugs is usually reversible upon cessation of treatment, and new therapies under investigation may prevent hair loss when administered to people receiving chemotherapy treatments.

Many drugs have been associated with temporary hair loss in a variable percentage of patients. It is important to remember that different people may react differently to the same drug, and hair loss may result in some people and not others.

Further Resources