A longer index finger is said to suggest lower prenatal Testosterone exposure and potentially lower current Testosterone levels. This theory lacks scientific evidence and is not an accurate measure of Testosterone levels.

Most studies agree that 2D : 4D is sexually dimorphic. In men, the 2nd digit tends to be shorter than the 4th, while in women the 2nd digit tends to be of the same size or slightly longer than the 4th. Nevertheless, here we demonstrate that the sexes do not greatly differ in the scaling between the 2nd and 4th digit.

The index finger, (also referred to as forefinger, pointer finger, trigger finger, digitus secundus, digitus II, and many other terms), is the first finger and the second digit of a human hand. It is located between the first and third digits, between the thumb and the middle finger.

Research suggests that having a longer ring finger compared to index finger reflects greater exposure to male hormones during an individual's time in their mother's womb. There are differences between and within sexes in finger lengths associated with relatively more masculine versus feminine development.