When you sneeze or cough any mucus or other fluids are projected forward and into the inside of the mask. When you exhale, the air pressure in the mask increase

When you sneeze or cough any mucus or other fluids are projected forward and into the inside of the mask. When you exhale, the air pressure in the mask increases and air is forced out the sides. No, these masks are not bio-safety level 4, but they're probably better than nothing. At worst they prevent a portion of your sneeze and cough ejecta from landing on surfaces around you.