Allergies occur when the immune system responds to a false alarm, attacking harmless materials like pollen, dust or mold. For practical purposes, allergies are split up into allergies to foods, chemicals (includes drugs), and inhalants (pollens and micro-organisms such as bacteria, mites, etc.). Inhalant allergies usually present with problems in the airways - rhinitis, sinusitis, itchy palate and/or throat, or asthma with cough, wheezing and shortness of breath.