Asian men with AGA display different characteristics compared with men of other ethnicity. However, there is an increase in prevalence with age among all the Asian groups studied similar to that observed in other ethnic population8-12,29
. The reason for this increase rate in the prevalence of AGA compared to Europeans remains unknown, but a transition toward a more Western diet and lifestyle may play a role.
There are also populational differences in the patterns of hair loss in AGA. In a previous study, FPHL was observed in 11.1% of Korean males with AGA8
. In a Chinese study, MPHL was found in 13 of 108 (12%) women with AGA, all of whom were over 50 years of age10
. In an Indian study, although it was possible to classify 80% of cases of AGA and II (28%) and III (15%) were the most common types of AGA, 27 patients of 150 male subjects (18%) did not fit into specific patterns according to the Norwood Hamilton classification30
. In addition, the type 'a' variant was noted in 20% of patients, clearly indicating the limitations of the existing classifications. There is considerable overlap in types IV, V and VI in the Norwood classification, with the 'a' variants further confusing the picture30
Various classification methods have been proposed for describing AGA. In 1950, Beek31
published a classification system, based on 1,000 males of European descent, which used two evolutionary aspects: frontal and frontovertical baldness. In the following year, the first systematic classification of AGA was established by Hamilton2
, who sub-classified patterns of baldness based on frontoparietal, frontal recession, and vertex thinning, then evaluated a large group of men and women for the presence of specific patterns of hair loss from the prenatal period through the tenth decade of life. In 1975, Norwood3
refined Hamilton's classification by emphasizing temporofrontal or vertex only subcategories of hair loss into seven types with a type A variant and reported the incidence of male pattern baldness at various ages in 1,000 adult male subjects of European descent. An additional pattern was introduced as the Norwood-Hamilton classification in a clinical trial of finasteride in MPHL32
proposed assigning separate designations (temporal, frontal, mid and vertex) to areas of the scalp that bald at different rates in different individuals with MPHL. Ludwig35
presented quite a different picture of hair loss in women from that described by Hamilton2
. He emphasized preservation of the frontal fringe despite progressive centrifugal loss over the top of the scalp and arbitrarily designated three gradations of hair loss. Olsen36
proposed that frontal accentuation (or the ''Christmas tree'' pattern) should be considered an additional pattern of hair loss in women, which helps to distinguish AGA from potential hair loss mimicries in women. Presently, the Norwood-Hamilton classification32
for MPHL and the Ludwig classification35
for female AGA are the most commonly used classification methods for assessing AGA worldwide.
Each of these existing classifications has substantial limitations in clinical setting. The Norwood-Hamilton classification ()3
is very detailed and is less stepwise classifications in its descriptions, making it difficult to memorize for common use. It does not list some non-typical types of baldness, such as FPHL in men. Additionally, many women with MPHL cannot be classified using the Ludwig classification system ()35
. For most of these classification systems, clinicians must use different classification systems for each gender in order to correctly classify patterns34
Fig. 1 The Norwood-Hamilton classification of male balding defines two major patterns and several less common types. Thinning starts in both temples as well as the crown/vertex and slowly progresses to encompass the entire top of the scalp (cited from Ref. 3 (more ...)
Fig. 2 The Ludwig pattern of hair loss (3-point). There are three main classes, each with increasing hair loss (cited from Ref. 35).
Thus, a more widely accepted, accurate, and stepwise method for classifying AGA would be of great benefit. Lee et al.37
devised a new classification system, named the Basic and Specific (BASP) classification (), which is comprehensive and systematic regardless of population or gender. The BASP classification37
was based on observed patterns of hair loss. The basic (BA) types represent the shape of the anterior hairline, and the specific types (SP) represent the density of hair on distinct areas (frontal and vertex). There are four basic types (L, M, C, and U) and two specific types (F and V). The final type is assigned according to a combination of the assigned BA and SP types.
Fig. 3 The BASP classification system includes four basic types (L, M, C, and U) and two specific types (V and F). The basic types represent the shape of the anterior hairline, and the specific types represent the density of hair on specific areas (frontal and (more ...)
A total of 2,213 Korean subjects, comprised of 1,768 males and 445 females, were classified according to the BASP classification37
. According to the severity of the phenotype, both the basic and specific types were subclassified into subtypes in order to generate a more stepwise and systematic classification. It is possible to describe patterns of hair loss in detail using the BASP method, and, thus estimate the further extent of hair loss and therapeutic response to a certain therapy. For both sexes, the majority of patients enrolled in the study were in the third and fourth decades of life (65.1% of males and 56.68% of females). In males, the older as well as the younger group were more likely to have little recession of the frontal hairline (classified as type M1-2) and diffuse thinning over the top of the scalp (type F1-2). The women in the study developed typical female AGA.
In men, regardless of age, 1,434 of the 1,768 males were classified as type M, accounting for 81.1% of cases. Among the subtypes and according to the severity of baldness, the majority of subjects below 50 years of age were classified as type M1, whereas most subjects over the age of 50 were classified as type M2. The incidence of Type L (9.3%) tended to decrease with age, but those of types C (5.8%) and U (3.8%) tended to increase. In women, type L showed the highest frequency in all age groups, accounting for 210 (47.2%) of 445 female subjects. Regardless of age, types M, C, and U were the next most common in order, observed in 121 women (27.2%), 111 women (25.0%), and 3 women (0.6%) of the 445 subjects, respectively. Type C0 was the second most common subtype in female subjects between the second and fourth decade of life, and its incidence decreased with age. In men, type F, which is identical to FPHL in the Ludwig classification, was observed in 42.4% (749/1,768) of male subjects, and type V was observed in 19.8% (350/1768). The grades of both types increased slightly with age. In women, type F was observed in 70.6% (314/445) of female subjects with AGA.
The BASP classification is a stepwise, systematic, and universal classification system for AGA, regardless of race or sex. It is an easily available comprehensive classification system. The BASP classification may prove particularly useful in communicating the exact amount and distribution of hair loss in those with AGA37
. For these reasons, we use the basic and specific (BASP) classification in this review.