The end of sponge-worthiness:
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.