While the engine air filter in your car is important, in most cars manufactured during the past decade or so there is another, little-known air filter that screens a different type of air - the air you breathe.
Thought automakers refer to them by different names, they are most generally known as cabin air filters. These filters work very similarly to the air filters that screen the heating / cooling system in your home, in that they screen the air that is circulated into your car's passenger compartment for dust, soot, pollen and other contaminants. Some high-end cabin air filters even contain a layer of activated charcoal that actually scrubs odors from the air, as well. The result is air that is much leaner that what would otherwise be pulled into the car. (Want proof? Try searching for "dirty cabin air filter" photos on the Internet to see just a few examples of the types of things drivers have been preveted from breathing thanks to their cabin air filters.)
However, just like any air filter, a cabin air filter will eventually become clogged with dirt or debris- or mice, according to a couple of the photos we came across! When that happens, your car's heating and air-conditioning system can have a harder time circulating air. Let the condition go long enough and the filter could tear, allowing all the nastiness it had carefully collected to come pouring into your car to be breathed by you and your family.
Car manufacturers typically recommend changing the cabin air filter at least once per year, so it's well worth asking your service advisor whether or not your car is equipped with a cabin air filter, and how long it has been since the filter was changed.
Source: godrivemag.com, Spring 2012