Since I don't get enough air breathing through the nose, I have to ride with open mouth. I try to concentrate to aat least grit my teeth.
Worst thing happening to me was when I hit a fence pole hidden in light dry snow. The following crash happend so unexpected and fast, I lost orientation and got stuck head down (vertical) with the arms bent backwards. Was very hard not to panik. Was glad to wear the face mask cause I'm shure my mouth was wide open while crasing.