Hair

The most common cause of balding, by far, is physiological. The firm terminal hair of mature adulthood is replaced by soft vellus hair—a relic of the first immature hair of infancy and early childhood. This process is under genetic control, with inherited influence on male-type hormones. The onset can be as young as seventeen in males and in the mid-twenties in females. In general, the areas that are the last to get terminal hair are the first to lose it (see Figure 2). The average of onset in males is in the late twenties and in females in the mid-thirties (see Figure 3).

Reversible hair loss. Physiological balding is not reversible, but there are other types of balding that are reversible. For example, the hair shaft can break because of fungal infection or from repeated peroxide bleaching.

Hair can fall prematurely from the follicle. This is termed telogen effluvium. It can follow an infective illness, or from some other mild toxic process that occurred six to eight weeks beforehand. The hair suddenly falls out in unusual amounts, leaving a thin scalp covering. Previously unnoticed physiological baldness may then be revealed, sometimes causing anxiety. Telogen effluvium is self-limiting, although in some cases the problem continues for a number of years before ceasing spontaneously. Rarer causes relate to hormone irregularity, particularly, thyroid hormones. Dietary factors, such as a general food deficiency, protein deficiency, low blood iron, or, more rarely, low zinc levels, are sometimes responsible. A sudden unexplained onset in older patients always raises concern of an underlying malignancy.

Alopecia areata is a harmless form of patchy baldness that can occur at any time of life. The hair ceases to grow in its mid-anagen cycle and falls out. Usually there are solitary or multiple round patches of baldness, but it can be widespread over the scalp, mimicking other forms of diffuse hair loss. When there is apparent loss of the hair follicle, this condition is termed scarring alopecia. Sometimes the follicle opening cannot be seen in normal balding. Burns caused by heat or chemicals can destroy the hair root, as well as some chronic inflammatory conditions. The cause of hair loss can be complex, and assessment by a knowledgeable physician is often required.