Mold allergies are the result of a fateful mistake on the part of your immune system. If your body accidently identifies the spores of a type of mold as harmful, it will keep making that mistake over and over. If you suspect that you have an allergy to mold based on symptoms like sneezing, congestion, runny nose, itchy and watery eyes, a visit to your doctor or an allergist may help with the diagnosis.
Before your doctor performs any allergy tests, he'll want to know your allergic history: what your symptoms are, when they affect you, whether other people in your family have allergies and so forth. He might also perform a physical exam to rule out other causes of your allergy-like symptoms. If the doctor thinks there's a fair chance that you have a mold allergy, he might conduct one of two tests -- or possibly both.
The skin prick test uses watered-down extracts of mold allergens to check your reactions. A little drop of the allergen-containing liquid is applied to the skin of your arm or back; then it's pushed into your skin with a little puncture or scratch. If a little bump develops on any of the spots, it indicates a likely allergy to that substance. Meanwhile, a blood test referred to as RAST, or radioallergosorbent test, checks to see how your blood responds to the introduction of suspected allergens. The doctor draws some of your blood and sends it to the lab where it's exposed to various mold allergens. Then the blood is checked for the presence of the antibody immunoglobulin E, which is what your immune system produces in an allergic reaction. If it's there, you're likely allergic to the mold you're being tested for.