An air purifier is a device which aims to free air from contaminants. The popularity of air purifiers spur from the results from environment researches which claim that the air inside homes are dirtier than the air outside of homes. Air purifiers are particularly beneficial for allergy sufferers and asthmatics or those who wish to reduce second-hand smoke. Various techniques are used in air purifiers in the current market to accomplish indoor air purification. These techniques include mechanical air filters, absorbents like charcoal, and electrostatic charges or ionizers. Additional air purifier setups include germicidal UV light and the emission of ions into the air to react with contaminants and making them harmless enough to breathe. When selecting air purifiers, consumers are influenced by several factors, including visual appeal, noise level, and frequency of filter replacement. There are many different types of air purifier filters, some air purifiers can be cleaned by water, by hand or by vacuuming while other air purifiers need to be replaced within a few months or a few years.