Molds belong to the kingdom Fungi. Molds reproduce by releasing “seeds”, called spores, in the air. These spores contain allergens. Inhaling these spores lead, in atopic human, to an allergic reaction. Spores spread mainly from spring to early fall. Due to the fact that fungi also lives indoor, allergic reactions will occur throughout the entire year. It is estimated that 3-10% of the population, worldwide, is sensitized to mold. From all of the mold species only a few can cause allergic reactions. One of these species is the Alternaria alternata (also know as Alternaria tenuis) which is abundantly present indoor and outdoor. A. alternata has allergens which contains both mycelial fragments and airborne spores which can cause allergic symptoms. Humans who suffer from mold allergy have an IgE reactivity roundabout 70% to Alternaria. A mold allergy can cause a severe respiratory reaction to persons with allergic bronchitis/ asthma.