Study author Gordon G. Gallup, Ph.D., a psychologist at the State University of New York in Albany, also found that women who routinely had intercourse without condoms became increasingly depressed as more time elapsed since their last sexual encounter. There was no such correlation for women whose partners regularly used condoms.
Gallup's survey of 293 college women also found that those who did not use condoms were most likely to initiate sex and to seek out new partners as soon as a relationship ended. "These women are more vulnerable to the rebound effect, which suggests that there is a chemical dependency," says Gallup.
Semen contains hormones including testosterone, estrogen, prolactin, luteinizing hormone and prostaglandins, and some of these are absorbed through the walls of the vagina and are known to elevate mood.
I'll bet some people might argue that this is an additional reason why women should use condoms: in order to protect themselves against depression (an unlabeled but powerful Sexually Transmitted Disease.) But I say that this is more evidence that attaching to your sex partner is the most natural thing in the world. We are playing with fire by trying to have sex without relationships. Using the condom to prevent the depression is just taking one step further away from the organic reality that sex naturally unites us with our partners, as well as makes babies.