DNA on bedding — does it prove intercourse?

No.

The presence of DNA on bedding does not, on its own, prove that intercourse occurred.

Bedding is a high-contact environment where biological material accumulates easily through everyday activities such as sleeping, sharing spaces, handling laundry, and contact with clothing or skin.

DNA may be present from prior contact, indirect transfer, persistence over time, or movement of biological material between items. Its presence does not establish when it was deposited or what activity led to its presence.

Even where semen is suspected or detected, this does not determine when it was left, whether it relates to the alleged event, or whether the contact was consensual. You can read more in a real case study here about how DNA evidence can be challenged in a sexual assault case.

Laboratory testing can identify DNA and sometimes link it to an individual, but it cannot determine the pathway by which the DNA arrived or the timing of deposition.