Cunnilingus during menstruation: remember that blood can pass more kinds of infections than other bodily fluids. Know your and your partners STI statuses, and get tested regularly. And of course, keep proper hygiene the endometrium's original purpose was to support and nourish life, and it will still do that once it has been shed. Lots and lots of tiny, smelly life. As my 10th grade biology teacher loved to tell us, bad hygiene makes the flora and fauna on your body really, really happy. Keep your microbiome in check.