Summary
A larger ratio of philtrum length to mouth length is considered a masculine feature, while a smaller ratio is a feminine one. Two studies have revealed distinct facial differences between males and females, especially concerning the philtrum (the groove between the nose and upper lip) and mouth. The first study by Shin et al. (2014) discovered that men typically have a longer philtrum and wider mouth than women. They also found that the difference in length and height of the philtrum is generally larger in men, indicating a higher ratio of philtrum length to mouth length – a masculine feature. Conversely, women tend to have a smaller philtrum length to mouth length ratio, seen as a feminine feature.
A separate study focused on young adults in Turkey and confirmed these findings. It also found significant gender-based differences in the ratio of philtrum length to upper lip height. Men usually have a larger ratio, with a longer distance from nose base to upper lip relative to their upper lip height, while women have a smaller ratio.
Research
According to the study by Shin et al. (2014), The features of the face, including the philtrum (the groove that runs from the bottom of the nose to the upper lip) and mouth, differ between males and females. A research has found that men generally have a longer philtrum (height of the philtrum or HP) and a wider mouth compared to women.
In men, the difference between the length of the philtrum and its height (termed as LPC and HP respectively) is generally greater than it is in women. In specific numbers, this difference is about 2.5 mm in men versus 0.8 mm in women. This means men tend to have a higher ratio of philtrum length to mouth length, making it a masculine feature.
On the other hand, women generally have a smaller difference between the length and height of their philtrum, leading to a smaller ratio of philtrum length to mouth length, thus making it a feminine feature.
Another study was carried out that compared the facial features of young adult men and women in Turkey to identify differences based on gender, focusing primarily on the lips and surrounding areas. Several points were measured on the face, including the heights of the upper and lower lips, the length of the philtrum (the vertical groove between the base of the nose and the border of the upper lip), and the width of the mouth.
Statistically significant differences were found in some of these measures between the sexes. The ratios calculated from these measurements were found to be larger in men than women in certain cases. One of these was the ratio of the length of the philtrum (sn-ls) to the height of the upper lip (ls-st). In simple terms, men in the study generally had a longer philtrum compared to the height of their upper lip than the women did.
What this means in everyday language is that in men, the distance from the base of the nose to the upper lip (the philtrum length) tends to be longer relative to the height of their upper lip, giving a larger ratio which is considered a masculine feature. On the other hand, women typically have a shorter distance from the base of the nose to the upper lip compared to the height of their upper lip, resulting in a smaller ratio, which is deemed a feminine characteristic.
Reference
Shin, K. J., Gil, Y. C., Song, W. C., Koh, K. S., & Choi, H. G. (2014). Morphometric analysis of the upper lip in Koreans. Facial Plastic Surgery, 30(05), 587-592. https://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-0034-1393698
Bahşi, I., Orhan, M., Kervancioğlu, P., Uçar, H., Karatepe, Ş., & Sayin, S. (2022). Lip Anthropometry of Healthy Turkish Young Adults. Journal of Craniofacial Surgery, 33(2), 696-700. https://pubmed.ncbi.nlm.nih.gov/34310423/