An allergy is an adverse reaction that the body has to a particular food or substance in the environment.
Some of the most common allergens include:
grass and tree pollen (hay fever)
animal dander (tiny flakes of skin or hair)
food allergy (particularly fruits, seafood and nuts)
medicines (including antibiotics such as penicillin)
Symptoms of an allergy are often mild and can include:
Anaphylaxis (or anaphylactic shock) is a severe allergic reaction. The reaction can be very fast, happening within seconds or minutes of contact with the thing a person is allergic to.
When anaphylaxis occurs, a chemical called histamine is over-produced, causing one or more life-threatening Airway, Breathing or Circulation problems.