An allergy is an inappropriate and sometimes life-threating immune response (reaction of the immune system). The term allergy is also known as hypersensitivity. People who have allergies often are sensitive to more than one thing. Substances that often cause reactions can be grouped as
- Food (and proteins comprised in food) 
- Insect stings
- Medicines (or common components of medicines such as sulfites)
- Latex (used in medical supplies like gloves)
- Mold spores
- Pet dander
- Dust mites
Allergists (scientist that study allergies) think both genetics and the environment contribute to the manifestation of allergies. Normally, your immune system fights germs. It is the body's God-given defense system against potential harm. In most allergic reactions, however, the immune system is attacking a normally harmless substance.
A severe allergic reaction such as swelling of the throat, lips and mouth and eventual obstruction of the trachea (called anaphylaxis) is life-threatening, immediate medical attention is required to save the victim's life.
Non-life threating allergic reaction symptoms can include: a runny nose, sneezing, itching, rashes, swelling of the skin, or asthma. Symptoms can vary. Allergies should not be confused with intolerances/food intolerances which are never life-threating. Although Food Intolerances (problems with digestion and metabolism of certain foods) can make one feel bad (by causing indigestion or bloating such as in a gluten intolerance), they are not fatal.
- Anna Richards (June 2015). The Allergy Epidemic. Healthy Food Guide, 40–44.
- Staci Nix (2017). Williams' Basic Nutrition and Diet Therapy (15th Edition). Elsevier/Lecturer, 70.
- Non-life threating Food Intolerances