This is where mold and mildew and other contaminants get trapped causing foul odors. A dirty evaporator also prevents a free flow of air through your vents. A dirty evaporator reduces the cooling efficiency when using your air conditioner.

Pictured is a single mold strand releasing its spores.

Following are excerpts from the EPA publication on mold. The publication is a treatise on the problem of mold in your living environment at home and office. The same information holds very true in the confines of the automobile environment.

You can find the complete publication at http://www.epa.gov/mold/moldguide.html

Molds are part of the natural enviornment. Outdoors, molds play a part in nature by breaking down dead organic matter such as fallen leaves and dead trees, but indoors, mold growth should be avoided. Molds reproduce by means of tiny spores; the spores are invisible to the naked eye and float through outdoor and indoor air. Mold may begin growing indoors when mold spores land on surfaces that are wet. There are many types of mold, and none of them will grow without water or moisture.

Can mold cause health problems?

Molds are usually not a problem indoors, unless mold spores land by a wet or damp spot and begin growing. Molds have the potential to cause health problems. Molds produce allergens (substances that can cause allergic reactions), irritants, and in some cases, potentially toxic substances (mycotoxins).

Inhaling or touching mold or mold spores may cause allergic reactions in sensitive individuals. Allergic responses include hay fever-type systems, such as sneezing, runny nose, red eyes, and skin rash (dermatitis). Allergic reactions to mold are common. They can be immediate or delayed. Molds can also cause asthma attacks in people with asthma who are allergic to mold. In addition, mold exposure can irritate the eyes, skin, nose, throat, and lungs of both mold allergic and non-allergic people. Symtoms other than the allergic and irritant type are not commonly reported as a result of inhalling mold.

Please note: Dead mold may still cause allergic reactions in some people, so it is not enough to simply kill the mold, it must also be removed.

Pictured: These are mold spores waiting to be picked up by the airflow and blown through the HVAC system and into your passenger cabin compartment. People with asthma and are sensitive to mold may suffer an asthma attack when the spores are inhaled.

Sneezing is not always the symptom of a cold. Sometines it is an allergic reaction to something in the air. Health experts estimate that 35 million Americans suffer from upper respiratory tract symptoms that are allergic reactions to airborne allergens. Pollen allergy, comonly called hay fever is one of the most common chronic diseases in the United States. World wide, airborne allergens cause the most problems for people with allergies. The respiratory symptons of asthma, which affect approximately 11 million Americans, are often provoked by airborne allergens.

Overall, allergic diseases are among the major causes of illness and disability in the United States, affecting as many as 40 to 50 million Americans.

The National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health (an agency of the U.S. Department of Health and Human Services) supports and conducts research on allergic diseases. The goals of this research are to provide a better understanding of the causes of allergy, to improve methods for diagnosing and treating allergic reactions, and eventually to prevent allergies.

Why are some people allergic?

Scientists think that some people inherit a tendency to be allergic from one or both parents. This means they are more likely to have allergies. They probably, however do not inherit a tendency to be allergic to any specific allergen. Children are more likely to develop allergies if one or both parents have allergies. In addition, exposure to allergens at times when the body's defenses are lowered or weakened, such as after a viral infection or during pregnancy, seems to contribute to developing allergies.

What is an allergic reaction?

Normally, the immune system functions as a body's defense against invading germs such as bacteria and viruses. In most allergic reactions, however, the immune system is responding to a false alarm. When an allergic person first comes into contact with an allergen, the immune system treats the allergen an invader gets ready to attack. The immune system does this by generating large amounts of a type of antibody called immunoglobulin E, or IgE. Each IgE antibody is specific for one particular substance. In the case of pollen allergy, each antibody is specific for one type of pollen. For example, the immune system may produce one type of antibody to react against oak pollen and another against ragweed pollen.

The IgE molecules are special because IgE is the only type of antibody that attaches tightly to the body's mast cells, which are tissue cells, and to basofils, which are blood cells. When the allergen next encounters its specific IgE, it attaches to the antibody like a key fitting into a lock. This action signals the cell to which the IgE is attached to release (and, in some cases, to produce) powerful chemicals like histamine, which cause inflammation. These chemicals act on tissues in various parts of the body, such as the respiratory system, and cause the symptoms of allergy.

Why are some people allergic?

http//www.niaid.nih.gov/publications/allergens/airborne_allergens.pdf