A classmate sent me what turned out to be a hoax story claiming an activity that I will describe simply as a fun activity shared between a man and one other person can actually prevent breast cancer. Sadly, it can't, but apparently a component can do lots of other good things:
[Psychologists Gordon] Gallup and [Rebecca] Burch reasoned that certain chemicals in human semen, through vaginal absorption, affect female biology in such a way that women who have condomless sex literally start to smell different from those women who do not—or at least, their bodies emit the pheromones that “entrain” menstrual cycles among cohabitating women. (Their hunch was indeed borne out by reviewing the existing literature on menstrual synchrony.) But this happenstance discovery of asynchronous lesbians was just the tip of the semen iceberg for Gallup and Burch, who quickly discovered that, although much was known among biologists about basic semen chemistry, virtually nothing was known about precisely how these chemicals might influence female biology, behavior and psychology.
... In fact, semen has a very complicated chemical profile, containing over 50 different compounds (including hormones, neurotransmitters, endorphins and immunosupressants) each with a special function and occurring in different concentrations within the seminal plasma. Perhaps the most striking of these compounds is the bundle of mood-enhancing chemicals in semen. There is good in this goo. Such anxiolytic chemicals include, but are by no means limited to, cortisol (known to increase affection), estrone (which elevates mood), prolactin (a natural antidepressant), oxytocin (also elevates mood), thyrotropin-releasing hormone (another antidepressant), melatonin (a sleep-inducing agent) and even serotonin (perhaps the most well-known antidepressant neurotransmitter).
It's always fascinating to me the sorts of things that pop up in random reading.