Performing oral sex or having sex without a condom may benefit both mental and physical health in women, according to scientists who analyzed the effects of semen's "mood-altering chemicals."

Researchers Gordon Gallup and Rebecca Burch, both from State University of New York at Albany, and psychologist Steven Platek of the University of Liverpool predicted that because the ingredients in semen include "mind-altering" drugs like mood-elevating estrone and oxytocin, affection-promoting cortisol, sleep-inducing melatonin and antidepressants prolactin, thyrotropin-releasing hormone and serotonin, women who have more unprotected sex should be less depressed than those who have protected sex.

Researchers conducted a survey assessing the sex lives and mental health of 293 college females from the SUNY-Albany campus.

All the female participants were asked to fill out an anonymous, written questionnaire about different aspects of their sexual behavior and to complete the Beck Depression Inventory, a commonly used clinical measure of depressive symptoms.

Researchers indirectly measured seminal plasma circulating in the woman’s body by how recently participants had sex without condoms.

Results from the study, published in the Archives of Sexual Behavior, showed that even after adjusting for frequency of sexual intercourse, participants who had sex and "never" used condoms showed significantly fewer depressive symptoms than women who "usually" or "always" used condoms when having sex.

Additionally, researchers found that sexually active women who never used condoms also had fewer depressive symptoms than women who abstained from sex altogether.

Surprisingly, really promiscuous women who used condoms were just as depressed as women who practice total abstinence, leading researchers to suggest that semen, not sex, makes women happier.

Previous findings also suggest that women exposed to semen perform better on concentration and cognitive tasks and that a woman's body is able to detect 'foreign' semen that differs from their long-term or recurrent sexual partner’s signature semen.

A woman's ability to detect foreign semen may be an evolutionary trait that prevents pregnancy from an unfamiliar source because it signals a disinvested male partner who is not as likely to provide for the offspring. 

Researchers noted that women who have unprotected sex with their partners may experience more significant depression after a break-up with than those who were not as regularly exposed to an ex-partner's semen.