Does DNA in the vagina prove intercourse?

The presence of DNA in the vagina does not, on its own, prove that intercourse occurred.

It should not be assumed that DNA detected in a vaginal sample originates from semen. DNA may come from a range of biological sources, including skin cells, saliva, fingers, or other bodily material deposited during contact.

DNA can also be transferred into the vaginal area indirectly. Transfer may occur via hands, clothing, shared surfaces, personal hygiene, or through the individual’s own actions. Biological material may also be introduced or moved during the process of medical examination and sampling.

In some cases, sperm cells are identified alongside DNA. In others, only DNA is detected. The presence of DNA alone does not establish its source, the pathway by which it arrived, or the activity that led to its presence.

Laboratory testing can identify genetic material and sometimes associate it with an individual, but it cannot determine when the DNA was deposited or whether it resulted from intercourse rather than another form of contact or transfer.