One of the marvels of the human body is that it can defend itself against harmful invaders such as viruses or bacteria. In some people, the body reacts to harmless substances such as dust, mold or pollen by producing an antibody called immunoglobulin E (IgE). When patients with one of the allergic diseases (such as rhinitis or asthma) are exposed to these substances, the immune system then rallies its defenses, launching a host of complex chemical weapons to attack and destroy the supposed enemy. In the process, some unpleasant and, in extreme cases, life-threatening symptoms may be experienced.