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Mold Allergy Facts

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When inhaled, tiny fungal spores, or sometimes pieces of fungi, may cause allergic rhinitis. Because they are so small, mold spores also can reach the lungs.

In a small number of people, symptoms of mold allergy may be brought on or worsened by eating certain foods such as cheeses processed with fungi. Occasionally, mushrooms, dried fruits, and foods containing yeast, soy sauce, or vinegar will produce allergy symptoms.

Where do molds grow?

Molds can be found wherever there is moisture, oxygen, and a source of the few other chemicals they need. In the fall, they grow on rotting logs and fallen leaves, especially in moist, shady areas. In gardens they can be found in compost piles and on certain grasses and weeds. Some molds attach to grains such as wheat, oats, barley, and corn, which makes farms, grain bins, and silos likely places to find mold.

Hot spots of mold growth in the home include damp basements and closets, bathrooms (especially shower stalls), places where fresh food is stored, refrigerator drip trays, house plants, air conditioners, humidifiers, garbage pails, mattresses, upholstered furniture, and old foam rubber pillows.

Molds also like bakeries, breweries, barns, dairies, and greenhouses. Loggers, mill workers, carpenters, furniture repairers, and upholsterers often work in moldy environments.

What molds are allergenic?

Like pollens, mold spores are important airborne allergens only if they are abundant, easily carried by air currents, and allergenic in their chemical makeup. Found almost everywhere, mold spores in some areas are so numerous they often outnumber the pollens in the air. Fortunately, however, only a few dozen different types are significant allergens.

In general, Alternaria and Cladosporium (Hormodendrum) are the molds most commonly found both indoors and outdoors in the United States. Aspergillus, Penicillium, Helminthosporium, Epicoccum, Fusarium, Mucor, Rhizopus, and Aureobasidium (Pullularia) are common as well.

There is no relationship, however, between a respiratory allergy to the mold Penicillium and an allergy to the drug penicillin, which is made from mold.

Are mold counts helpful?

Similar to pollen counts, mold counts may suggest the types and number of fungi present at a certain time and place. For several reasons, however, these counts probably cannot be used as a constant guide for daily activities.

One reason is that the number and types of spores actually present in the mold count may have changed considerably in 24 hours because weather and spore distribution are directly related. Many common allergenic molds are of the dry spore type—they release their spores during dry, windy weather. Other fungi need high humidity, fog, or dew to release their spores. Although rain washes many larger spores out of the air, it also causes some smaller spores to be propelled into the air.

Learn more information about allergies by type, and methods to prevent and treat them.

Allergies: Did You Know

Health experts estimate that 35 million Americans suffer from upper respiratory tract symptoms that are allergic reactions to airborne allergens.

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