Pollen filters, also referred to as cabin filters, remove almost all airborne pollutants before entering the passenger compartment. This includes dirt, dust, pollens, vehicle exhaust emissions, sulphur dioxide, soot, tyre rubber, brake dust and other harmful substances. In addition to particle filtration, the addition of activated charcoal in some filters can remove gases and odours. Once considered a luxury, the pollen filter has become a necessity for an increasing number of motorists and their passengers who may suffer from asthma, allergies or other respiratory problems.