even when they use a condom, a new study suggests. In the study, researchers had 12 monogamous heterosexual couples collect swab samples after a period of abstinence and then shortly after having sex.

Analysis showed that a participant’s unique bacterial signature could be identified in their sexual partner’s sample following intercourse. Three of the couples reported using a condom.

Analysis showed that a participant's unique bacterial signature could be identified in their sexual partner's sample following intercourse. Three of the couples reported using a condom.