Most of these materials are completely harmless to non-sufferers. When it subsequently encounters the allergen, the mast cell breaks apart and releases a chemical called histamine. It is histamine that produces the characteristic symptoms of allergic reactions. These symptoms will vary in type and severity from case to case, and depending on the area of body that has been exposed to the allergen. Allergies to food usually lead to vague itching in the mouth and throat when the food in question is eaten.
Many people have difficulty distinguishing an allergic reaction from a cold.
While a cold will usually surface for three to five days and then disappear, untreated allergies will usually resurface periodically for years or manifest themselves as constant cold-like symptoms. The most severe symptom of allergies occurs when histamine is released simultaneously all over the body. This kind of systemic allergic reaction often leads to a condition called anaphylaxis, which is extremely serious and can be fatal if not swiftly and appropriately treated. Some people, for example, are extremely allergic to bee or wasp stings, and must carry a self-injecting syringe containing epinephrine, a chemical that, when decisively applied, can literally save one's life in the event of an attack. Anaphylactic symptoms include severe anxiety, headache, nausea, uncontrollable sneezing, abdominal cramps, shortness of breath, convulsions, and, if not treated quickly, loss of consciousness and eventual death.