It’s absolutely sanitary! And, no, you’re not going to get an STD from having cum on your face or from not washing your face after sex…
If your partner has an STD or another communicable disease then you’ll get it from engaging in any form of unprotected sex – oral or intercourse. It has nothing to do with you leaving cum on your face for too long or something, haha.
Don’t worry about it. Just wipe it off with the back of your hand or on her thighs or her stomach or even the sheets, and keep on going! It would actually be incredibly insulting/rude if you just left right after eating her out to wash your face… Sex gets messy and good sex is even messier! Enjoy it!
On the flip side, semen actually contains properties that are really good for your skin! Weird but true…