Is There an Indicator for Sexual Behavior in Patients with Borderline Personality Disorder? Study Investigates

Borderline personality disorder (BPD) is a complex psychiatric disorder, most notably characterized by instability in emotion, relationships, and self-image and affecting around 1%-2% of the general population. Women diagnosed with BPD often experience higher than average sexual dissatisfaction, depression, and orgasmic dysfunctions. However, they also tend to have higher than average sexual assertiveness, self-esteem, eagerness to engage in sexual contact outside of their relationships, and risky sexual behavior or impulsive sexual reactions.

Sexual impulsivity can be tied to seemingly uncontrolled initiation of new sexual relationships and a high number of sexual encounters. Previous research has shown that a person with BPD may have more sexual partners in their lifetime than a non-BPD counterpart. Conversely, they may also follow a pattern of withdrawing from or avoiding sex more so than their non-BPD counterpart. Really, there hasn’t been much investigation into the sexual response of women with BPD.

It’s understood that testosterone is a key hormone to the formation of brain circuits and central nervous functions in fetuses, as well as sexual functions and other behaviors presented later into adulthood. The amount of testosterone in the amniotic fluid during fetal brain development peaks around the 12-18 week point in gestation, and its level is believed to be a factor in the development of personality disorders. Furthermore, the 2D:4D ratio, which is the ratio of the lengths of the second (index) finger and fourth (ring) finger, becomes fully formed around week 14 of gestation – right during the peak of testosterone levels – and doesn’t change throughout life. It’s believed that BPD women will have a 2D:4D ratio similar to a non-BPD man, supporting the association of BPD women having higher levels of testosterone exposure during brain development. Typically, males will have a ratio of around .98, and females around 1.

While there has been previous interest in the 2D:4D ratio as an indirect indicator of testosterone exposure during brain development, there is very limited research on sexual behavior in women diagnosed with BPD based on this ratio. Indirect indicators could be useful for investigating prenatal brain development effects on sexual behavior. Direct indicators would pose an ethical challenge to study, as there would likely need to be testing during pregnancy. Consequently, a group of researchers set out to investigate the biologically conditioned sexual behavior of women diagnosed with BPD compared to women without this diagnosis. Specifically, they looked at the 2D:4D ratio and its correlation to sex hormones that were present in the amniotic fluid during brain development.

Between 2014 and 2019, 33 women diagnosed with BPD (average age of 25 years) and 56 women without a BPD diagnosis (average age of 20 years) had their 2D:4D ratio measured and were tasked with completing a questionnaire to assess their sexual functioning. Most of the members of each group identified as heterosexual, with the second most prominent sexual orientation being bisexual. Women with BPD also claimed they had more lifetime sexual partners than the women without BPD.

The 2D:4D ratio was measured on the palm side of both hands, from the midpoint crease to the tip of each second and fourth fingers (index and ring). The length of the index was then divided by the length of the ring to find the 2D:4D ratio of each hand. The questionnaire used to assess sexual functioning was the Arizona Sexual Experience (ASEX) questionnaire, which was rated on a scale of 1 (extremely strong/easily) to 6 (absent/never), with a higher score suggesting more severe sexual dysfunction. The questions asked were about sex drive, vaginal moisture upon arousal, and how easily they become aroused.

The 2D:4D ratio difference between both groups of women was found statistically significant in the right hand only, with BPD women having lower ratios than non-BPD women. This falls in line with previous literature which says the right hand is more sensitive to fetal sex hormones than the left. The lower ratios are more in line with the typical ratio for males, indirectly indicating a higher level of testosterone in the amniotic fluid during brain development.

As far as ASEX results go, the women with BPD tended to fall to the extreme side of the rating scale, while the women without BPD tended to fall closer to the middle of the scale. For example, when asked how easily they are sexually aroused, women with BPD answered more often with the “extremely easy” or “very easy” scores as well as the “very difficult” and “never” scores. Meanwhile, women without BPD tended to answer “somewhat easy” and/or “somewhat difficult.” This suggested that women with BPD likely have more extreme reactions to sexual behavior and more extreme sexual function or dysfunction than women without BPD.

This study attempted to find an indirect indicator of prenatal hormone consumption from amniotic fluid on the formation of the brain and conditioning of sexual behavior in women with BPD. Researchers found that the number of lifetime sexual partners, sexual activity, sexual arousal, and vaginal lubrication were correlated with the 2D:4D ratio of the right hand, suggesting that this may be a good indirect indicator of sexual functioning in women with BPD, and potentially an indicator of testosterone consumption during brain formation. While these findings offer intriguing insights, further research is necessary to better understand the complex interplay of biological, psychological, and social factors that shape sexual behavior and function, which cannot be attributed solely to prenatal exposure to sex hormones.

References:

Holka-Pokorska, J., & Kucharski, A. (2025). The assessment of the sexuality of patients with a borderline personality disorders based on their 2D:4D digit ratio. Sexual Medicine Open Access, 13(1). https://doi.org/10.1093/sexmed/qfaf006