Allergies are an overreaction of the body's natural defense system that helps fight infections (immune system). The immune system normally protects the body from viruses and bacteria by producing antibodies to fight them. In an allergic reaction, the immune system starts fighting substances that are usually harmless (such as dust mites, pollen, or a medicine) as though these substances were trying to attack the body. This overreaction can cause a rash, itchy eyes, a runny nose, trouble breathing, nausea, and diarrhea.
An allergic reaction may not occur the first time you are exposed to an allergy-producing substance (allergen). For example, the first time you are stung by a bee, you may have only pain and redness from the sting. If you are stung again, you may have hives or trouble breathing. This is caused by the response of the immune system.
Most people will have some problem with allergies or allergic reactions at some point in their lives. Allergic reactions can range from mild and annoying to sudden and life-threatening. Most allergic reactions are mild, and home treatment can relieve many of the symptoms. An allergic reaction is more serious when severe allergic reaction (anaphylaxis) occurs, when allergies cause other problems (such as nosebleeds, ear problems, wheezing, or coughing), or when home treatment doesn't help.
Types of allergies
There are many types of allergies. Some of the more common ones include:
Allergies that occur for more than 9 months out of the year are called perennial allergies.
Check your symptoms to decide if and when you should see a doctor.
eMedicineHealth Medical Reference from Healthwise
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