Gas mask protects the wearer from breathing harmful gases or particles into the lungs. The mask fits tightly over the face. Air can enter only through special filter pads that purify and filter the air. Activated charcoal purifies the air by trapping toxic gases and vapors. Particulate filters can remove particles of smoke, dust, and even some harmful biological agents. The purifying materials are in the cheeks of present-day masks, which are often part of an entire protective suit. Older models had a breathing hose attached to a canister.