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Allergies occur when your body mistakes a normally harmless substance (called an allergen) for a threat and attacks it. Your body will release a specific antibody called Immunoglobulin E (IgE) which causes the release of inflammatory chemicals such as histamine. Histamine causes the symptoms commonly associated with an allergic reaction, such as sneezing, runny nose, hives and watery eyes.

In order to treat your allergy symptoms, your doctor will first need to figure out what you are allergic to. This is usually done through a skin test, a blood test or a challenge test.

A skin test involves placing a small amount of what you may be allergic to (called an allergen extract) on or below the skin. There are three types of skin tests: a skin prick test, an intradermal test and a skin patch test.

A skin prick test requires a drop of the allergen extract to be placed on the skin, and a needle is used to either scratch or prick the skin through the drop. This allows the extract to enter the skin. After 15 minutes, any red, raised and itchy areas that have developed are measured. This is usually an indication that you are allergic to the allergen.

An intradermal test is more sensitive so it is performed after the skin prick test has come back negative but an allergy is still suspected. The allergen extract is injected into the skin. After 15 minutes any red, raised and itchy areas are measured.

A skin patch test is used to test for contact dermatitis, a skin allergy. A small pad with the allergy extract is taped to the skin for 24 to 72 hours. Any red or itchy areas are measured afterwards. This reaction indicates an allergy.

A blood test is used to measure the amount of allergy specific IgE antibodies in your blood. Unlike skin tests where the bigger the reaction, the more allergic you are, a blood test cannot tell you the degree to which you are allergic. This test is used when the individual’s skin is too sensitive for a skin test, if they cannot stop taking medications that will affect the results of a skin test or they are too allergic and a skin test could result in a life-threatening reaction.

A challenge test is used to rule out an allergy. This test involves ingesting a small amount of what you are allergic to in order to see if you still have a reaction. This test is usually performed with food or medications in a medical setting to make sure if you do have a reaction, it can be treated quickly.

Typically, the symptoms of an allergic reaction vary depending on what you are allergic to and how you are exposed to the allergen. If you breathe in pollen your eyes, nose and lungs may show symptoms. Whereas, if you eat something you are allergic to, symptoms will typically develop in your mouth, stomach and intestines.

Allergy symptoms can range from mild to life threatening. The level of severity depends on your level of sensitivity. Mild symptoms, such as those from seasonal allergies, can consist of a runny nose, itchy eyes, sneezing, stuffy nose and fatigue. Moderate symptoms, such as those from a pet allergy, can consist of nasal congestion, coughing, red and watery eyes and a skin rash. Food allergies and insect stings are the most likely to produce severe or life threatening symptoms. The symptoms for this level of reaction include hives, itching, redness, swelling, dizziness, vomiting, unconsciousness and cardiac arrest.