Weather seals and gaskets on a car's door and windows can erode over time and allow moisture or water into the vehicle. This is very common in older antique or restored autos or those left sitting or in storage for long periods of time. The other common area for mold infestation is the ventilation system.This is generally caused by blocked or clogged water lines from the car's condenser unit.

Once you've eliminated the source of the moisture getting into your car, truck or SUV, proceed with the Steps for Removing Auto, Car and Truck Mold.

Most molds found indoors – and a car is an indoor environment - are commonly called mildew and are plant-like organisms that grow along surfaces and that require food and moisture. Paper, leather, cardboard, cloth, and even dust on solid surfaces like glass, metal and plastic can support mold growth.

A small patch of mold can cause a musty odor, but surfaces can be spotted with mold growth that has little or no odor. Breathing in living or dead mold spores can cause health symptoms, though, so you don’t want mold to remain in spaces where you spend time – and some people spend a lot of time in their cars, especially if they use it to drive to work.

Mold can grow on biodegradable dust on solid surfaces, as well as in dust captured in carpeting and upholstery. Mold can also grow in the dust and plant litter inside the car’s heating or cooling system.

Your car operates in the outdoor environment where it rains or snows, depending on your climate; and where rain or humid air at the exterior enters the vehicle’s windows. Rain may enter the interior because weather seals and gaskets on the door, windows and trunk have eroded over time, or there are gaps or openings in the car’s exterior due to age, rust or damage done in an accident. And when you get in and out of the car with damp shoes, you may introduce moisture into the carpet, which is the most likely place in the vehicle for microbial growth. If your car does not have a cabin air filter, biodegradable debris like leaves and pollen can accumulate on the A/C coil. The condensate drain line can then get clogged, causing the unit to leak onto the carpet; or there may be a water-hose leak.