Dude?

What did they find?
The results showed that sexually active women who never used condoms showed significantly fewer depressive symptoms and also slept better than women who always or usually used condoms, says Sara C. Nelson at The Huffington Post. The findings also indicated that the women in the study who described themselves as “promiscuous” yet regularly used condoms were just as depressed as women who were abstinent. “The team says this suggests it is semen, not just sex,” that is raising some women’s happiness levels. Caveat: “Happiness” is a notoriously complex emotion that can be affected by any number of factors.

Why is this?
One prevalent theory is that a woman’s body can detect and recognize semen from long-term or recurrent partners. From an evolutionary standpoint, there’s an advantage to a mate’s sperm triggering chemical feelings of affection and feelings of closeness.