According to the American College of Allergy, Asthma & Immunology, if you come in contact with something to which you are allergic, your immune system considers it dangerous and releases a chemical called 'histamine' to counteract it.
The release of histamine can cause a variety of symptoms, including a skin rash, headache, sneezing, runny nose, swelling, nausea and diarrhea. The most severe reaction, known as anaphylaxis, can be life-threatening.
Substances that often cause allergic reactions are:
Pollen
Dust mites
Mold spores
Pet dander
Food
Insect stings
Medicines
Learn the types of allergies including food allergies, seasonal allergies, pet allergies, and many more at WebMD.
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