Top Allergy and Asthma Triggers -- and How to Avoid Them

by Stephanie Welch Alexander

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Mold
Molds -- parasitic, microscopic fungi lacking stems, roots or leaves -- can make allergy-sufferers pretty miserable. As many as 250,000 mold spores can fit on one pin head, and they are found both indoors and outdoors. Levels peak in late summer and fall months.

Outdoor molds usually grow in moist shade areas (soil, decaying vegetation, leaves and rotten wood); indoor molds are usually found in dark, humid areas of the home (basements, cellars, attics and bathrooms). Mucor, Aspergillus and Penicillium are common indoor molds.