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. The probability of developing an allergy increases if one or both parents also have allergies.
Allergies often vary as a function of age or physiological status.
Symptoms of allergy can be reduced by desensitization therapies. Although the term food allergy is widely used for any adverse reaction to food, only rarely is the immune system involved. The most common adverse reactions to food are toxic reactions and food intolerance. Natural foods, not additives or artificial flavors, are the basis for the majority of food allergies. The introduction of new proteins into crops has raised concerns that proteins with allergenic properties might be introduced unknowingly into genetically modified plants.