The second and subsequent exposure to the allergen results in symptoms. The type of symptom that develops depends on the specific allergen, the part of the body where exposure occurs, and the way the immune system reacts to the allergen. When an allergen enters the body of a person with a sensitized immune system, it triggers antibody production. Histamine and other chemicals are released by body tissues as part of the immune response. This causes itching , swelling of affected tissues, mucus production, muscle spasms , hives and rashes , and other symptoms.
Symptoms vary in severity from person to person.
The part of the body contacted by the allergen will, in part, also affect symptoms. Food allergies often include abdominal pain , cramping, or similar symptoms, although the whole body may be affected when the food is absorbed. Allergies to plants often cause skin rash . Drug allergies usually involve the whole body. Many disorders are associated with, triggered, or worsened by allergies.