Allergies happen when the immune system reacts to a foreign substance that gets inside the body. These substances are known as allergens. They include pollen, bee venom and pet dander. Allergies also can happen due to certain foods and medicines that don't cause reactions in most people. Allergic reactions happen when you come into contact with an allergen. Your immune system reacts by releasing histamines and other chemicals into your blood, causing symptoms that can irritate. Allergies are your immune system’s overreaction to foreign substances. When you touch, inhale or eat something you’re allergic to, your body thinks it’s harmful and reacts to try to get rid of it. This can cause minor reactions like itching, sniffling and sneezing. Find out about allergies, including typical symptoms, common allergies, when to get emergency medical help and allergy testing and treatments. Eye Allergies Known as allergic conjunctivitis, these reactions cause red, itchy, watery, and swollen eyes. They are common in people with seasonal allergies. Anaphylaxis: The Severe End of the Spectrum Anaphylaxis is a rapid, systemic allergic reaction that can be fatal without immediate intervention. What is an allergic reaction? Allergic reactions are a set of symptoms that happen after you touch, inhale or eat something you’re allergic to. They can also happen after a bee sting. Examples of allergens that can set off allergic reactions include pollens, pets, dust, foods and medications. An allergic response is a hypersensitive immune reaction to a substance that normally is harmless or would not cause an immune response in everyone. An allergic response may cause harmful symptoms such as itching or inflammation or tissue injury. The mechanism of allergic reactions involves immunoglobulin E antibodies (IgE) binding to an allergen and then to a receptor on mast cells or basophils, where they trigger the release of inflammatory chemicals such as histamine. [16] Diagnosis is typically based on a person's medical history. [3] The meaning of ALLERGIC is of, relating to, affected with, or caused by allergy. How to use allergic in a sentence. Allergic reactions (hypersensitivity reactions) are inappropriate responses of the immune system to a normally harmless substance.