An allergy is an inappropriate reaction of the body to one or more foreign substances that in the majority of people cause no symptoms. An allergic response involves the over-production of specific types of antibodies by the body's immune system. Allergic responses may be triggered by inhalation, dermal, or oral routes of exposure.
Food allergies are much less frequent.
Many different substances can cause an allergenic reaction. The most common are from natural sources, such as pollen, grasses, weeds, dust, certain foods, drugs and insect bites. Allergenic symptoms may include sneezing, rashes, coughing, stomach irritation and difficulties breathing. Asthma is also due to an allergenic reaction. Generally, susceptibility to allergy is an inherited trait.