The mask problem is particularly vexing because unlike simple surgical or homemade masks, the N95s block at least 95% of very small airborne particles, including those too tiny to be blocked by surgical or cloth masks. Airborne viral particles are considered one way the virus transmits, and are a particular risk in hospitals where ventilators and other respiratory treatments can lead to aerosolized particles. These masks are also fitted specifically for the wearer, forming a tight seal against the face. Because health care workers and emergency responders encounter the virus repeatedly, they need high-quality protection.