Clinical characteristics and factors associated with different BASP subtypes of androgenetic alopecia.

Background: This study aimed to explore the associated factors for different basic and specific (BASP) classification subtypes of androgenic alopecia (AGA). Methods: This retrospective case-control study included patients diagnosed with AGA in the Department of Dermatology of our hospital between May 2018 and June 2024 and healthy individuals undergoing routine physical examination during the same period. Ultimately, 1,505 patients with AGA and 1,751 healthy controls were enrolled. AGA was classified into M-, C-, U-, F-, and V-type according to the BASP classification system. Baseline differences between the AGA and control groups were first assessed using univariate analyses. Given the multiple comparisons involved, Bonferroni correction was applied to the univariate analyses. Subsequently, multivariable logistic regression was performed to identify factors independently associated with overall AGA, and multivariable regression analyses were further conducted to determine factors independently associated with the severity of each BASP subtype. Results: Compared with healthy controls, patients with AGA were more likely to be male, older, and smokers and to have a parental history of hair loss, higher BMI, shorter shampooing intervals, scalp oiliness, a high-fat diet, heart disease, hyperlipidemia, fatty liver, lower serum 25-hydroxyvitamin D [25(OH)D] levels, and higher homocysteine (Hcy) levels. In multivariable logistic regression, male sex, age, smoking, paternal and maternal hair loss history, BMI, shampooing interval ≤1 day, scalp oiliness, high-fat diet, heart disease, hyperlipidemia, fatty liver, lower 25(OH)D, and higher Hcy remained independently associated with AGA. In multivariable analyses of BASP subtype severity, age, father's hair loss history, high-fat diet, lower 25(OH)D, and higher Hcy were consistently associated with severity across all five BASP subtypes. Additional subtype-specific associations were also observed, including male sex for M-, U-, and F-type; drinking for U-, F-, and V-type; hypertension for U- and V-type; diabetes for F-type; hyperlipidemia for F- and V-type; and fatty liver for U-type. Conclusion: Several demographics, familial, lifestyle, and metabolic factors were independently associated with overall AGA, and both shared and subtype-specific associations were identified for the severity of different BASP subtypes. These findings may help inform clinical assessment and future hypothesis generation; however, prospective studies are still required before these associations can be interpreted in a temporal or causal framework.