The relationship between the second to fourth digit ratio and acne vulgaris

Although the pathophysiology of acne vulgaris (AV) is not clear, androgens are thought to play an important role in its development through either an increased level of circulating androgens or end-organ sensitivity. The ratio of the length of the second and fourth digit (2D : 4D) has been hypothesized to reflect prenatal androgen exposure and/or an individual's sensitivity to androgens, with a low 2D : 4D ratio suggesting high prenatal androgen exposure. Interestingly, the prenatal androgen peak time period coincides with both the development of the sebaceous gland and digits.

To determine the relationship between digit ratio and AV.

Vernier caliper was used to take digit measurements of both patients and controls. Acne severity was assessed by using the International Consensus Conference on Acne Classification System.

Data of 251 patients with AV (67.7% female) and 120 healthy controls (72.5% female), aged 16-40 years, were analysed. The 2D : 4D ratios of female patients with AV were significantly lower than healthy females in both hands. However, there was no significant difference between male acne cases and controls. Acne severity was positively correlated with the left 2D : 4D ratios and mean 2D : 4D ratio, whereas the duration of acne was negatively correlated with the right 2D : 4D ratios in females.

Our results support the anatomical evidence of in utero androgen exposure and/or an individual's sensitivity to androgens in patients with AV and suggest that the 2D : 4D ratio might be a predictor of acne development, duration, and severity grade, at least in female patients.