There is no valid medical proof saying that a woman puts herself in danger when she is menstruating and has sex. In fact, many women who get period-related pain claim orgasms help ease their cramps. Some women don' t like to have sex while menstruating, others do. On the other hand some partners of menstruating women don't mind a bloody mess, others do. What matters is the comfortability of both partners when this subject arises.
Many women use tampons and let their partners perform oral sex.
Others do the same plus use a dental dam or type of other barrier. Others use a male or female condom. Others actually like the blood or don't mind it and use nothing. Also, if you have sex with no barriers when menstruating, you may want to use old sheets or fuck in the shower. Every Saturday afternoon, SFSI posts its latest Ask-Us column answering any question you have about human sexuality.