Specialists receive retraining annually on how to properly fit these respirators around the nose, cheeks and chin, ensuring that wearers don’t breathe around the edges of the respirator. “When you do that, it turns out that the work of breathing, since you’re going through a very thick material, is harder. You have to work to breathe in and out. It’s a bit claustrophobic. It can get moist and hot in there,” Schaffner said.