For oral sex on a woman, preventing the transmission of disease is much more difficult. Some people recommend using dental dams, which are small squares of latex, or a sheet of plastic wrap held over the woman’s vagina during oral sex. But the odds of keeping the dental dam in place, so no bodily fluids are exchanged during passionate sex, seem pretty remote. And plastic wrap, which is so thin, seems likely to break, although some brands are stronger than others. Very thin underwear (you can even get an edible variety that comes in flavors) can also act as a barrier.