Filter in air purifiers are used to reduce the concentration of contaminants (including dust, pollen, pet dander, mold spores, dust mite feces, smoke particles and volatile organic compounds) found in the environment. These contaminants can act as allergens and pose a health risk. So, air purifier is useful and even necessary for people.

Internal combustion engine air filters

The combustion air filter prevents abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination. The air filter is also used to muffle the sound of the engine intake system. Most fuel injected vehicles use a pleated paper filter element in the form of a flat panel.