The most common cause of hair loss in men is called pattern baldness (also called androgenetic alopecia or AGA). This is presented by the loss of hair over the top (vertex) of the scalp. In this case, the specific mode of inheritance remains unknown although the term pattern baldness denotes that both genetic predisposition and the presence of androgens are necessary to cause expression.

Varying incidents of pattern baldness in men induces an early hair loss phenomenon that may take place any time after puberty. In this stage, serum androgen levels in men become naturally higher than in younger years. The progression of men’s hair loss through pattern baldness occurs in a distinct pattern. On the affected areas, the transition from large thick-pigmented terminal hairs to thinner, shorter, indeterminate hairs and finally to non-pigmented vellus (fine) hairs gradually takes place.

A crucial clinical examination of the scalp shows the extent and trend of the hair loss process:

• The first change in men with pattern baldness is usually seen with 96% of sexually matured male Caucasians including those who are not destined to progress in further hair loss. This case is called bitemporal recession. It comes through a gradual thinning in the temporal areas followed by progressive thinning in the frontal and vertex areas of the scalp.
• Recession of the frontal hairline is common.
• The frontal and vertex thinning areas may unite together resulting to the loss of hair all over the crown.

The cases of hair loss in men become higher over the years, although the rate can vary dramatically from person to person. It may also vary significantly over time. The intermediate evolutionary stages between minimal thinning and the stage when only a narrow horseshoe shaped band remains exist because of the decrease in hair density. The hair density of a normal person varies between 200 and 400 hairs/ sq cm while the hair density of a person affected by pattern baldness is 50-150 terminal hairs/ sq cm.

No one can tell what type of hair loss pattern a young man with early pattern baldness may assume. Generally, men who began losing hair in the second decade are those with whom alopecia will be most progressive. Initial male pattern hair loss in some men may be delayed until the late third to fourth decade.

The key to understanding the clinical presentation of pattern baldness is to know the dynamics of hair follicle cycling in normal as well as balding scalp. A normal scalp has several years average duration of the anagen (growth) phase of hair, while the telogen (resting) phase lasts 3 months. However, the pattern hair loss in men has an altered growth cycle that results to a progressive reduction in the duration of the anagen phase. Consequently, there is production of short, thin, hypo-pigmented, insignificant wisps of hair, and the condition becomes visible through the loss of scalp hair.

Classification Pattern Hair Loss in Men

According to the classification developed by Hamilton and Norwood, the clinical appearance of pattern baldness in most men is widely and instantly recognizable. These classifications were based on the degree of hair thinning and the affected areas of the scalp.

Hamilton established a classification based on eight evolutionary aspects and three sub-groups. He also made a comparison between the cases of the Caucasians and the Chinese. In 1975, Norwood recorded enhancements on the classification that Hamilton established and made a more detailed categorization, which is widely used today. He divided androgenetic hair loss in men into two common patterns: the Regular Type, characterized by hair loss that begins in two different areas - the temples and the crown. These two gradually merge into one. The Less Common Type is characterized by "front-to-back" hair loss. In 1976, Bouhana proposed a simplified classification of 5 evolutionary phases which come from two sub-groups. This classification allowed a more detailed evaluation of the surgical indications of hair transplantations in treating pattern baldness.

The scientific way of determining the rate or amount of the degree of baldness in patients is to compare the patient’s balding pattern with the standard patterns described by Norwood, which depict the most common configurations of male pattern baldness. There are seven grades of hair loss in the main series and five grades of a variation called the "A" series. As a rule, the pattern of a person’s hair loss follows the specific type first presented. In other words, a person who begins as a Class 2 usually evolves into a Class 3, then a Class 4, etc. A Class 2a becomes a Class 3a and then a Class 4a, and so on.

Other Facts about Male Androgenetic Alopecia

The occurrence of hair loss pattern in pattern baldness is characterized by both racial and age-related differences. Studies show that sexually mature Oriental and Native American men tend to have more preservation of the frontal hairline where baldness and less extensive baldness usually occur in the first place. Observation also shows that African-American men may have a lower incidence and extent of baldness with decreased frequency in fronto-parietal loss.

The vertex balding seen in men is rare in women. On the other hand, female pattern of balding is not uncommon in men, the frequency being higher in Asian men.