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What are allergies?

Allergic symptoms result from your body’s reactions to substances that your body sees as foreign to the body. Substances that can cause an allergic reaction are called allergens.

How do they occur?

Your immune system is your body's natural defense against bacteria, viruses, and other foreign substances. Before you can have a reaction to a particular substance, your immune system must first be sensitized to it. Usually this means your body has to have been exposed to the substance at least once before. Once sensitized, your body will react every time you have contact with the substance.

Many substances can cause an allergic reaction. The most common are:

  • pollen
  • mold
  • animal dander
  • dust and dust mites
  • latex
  • medicines
  • insect stings
  • foods.

Allergens may cause different kinds of reactions. The most common allergic conditions are hay fever, asthma, skin allergies, and eczema.

  • Airborne allergens such as mold and the pollen of trees, grasses, and weeds cause hay fever.
  • Pollens, molds, house dust, animal dander, and medicines can trigger asthma attacks. They can also cause year-round congestion, more mucus in your nose and airways, and an itchy, runny nose.
  • Allergic reactions of the skin can have many possible causes. Examples of irritants that can cause allergic reactions when they touch your skin are hair or skin care products, nickel in jewelry and belt buckles, dyes in leather or fabric, and poison ivy or poison oak.
  • Eczema is a skin problem that may be caused by allergens. It often happens in people who are prone to allergies and asthma. It causes itching, dryness, and fine scales or flaking. Sometimes it causes mild redness.

It’s also possible to have an allergic reaction to sunlight or temperature extremes.

Common foods that may cause allergy symptoms are shellfish, eggs, milk, nuts, and peanuts. Food allergies often occur in children, who may outgrow them.

It is not known why some people develop allergies. Allergies run in families. However, not every family member may be allergic to the same things or have the same reactions. Some may have hay fever. Others may have asthma or eczema. Others may have all of these allergic reactions.

Sometimes an allergic reaction may be severe. This is called anaphylaxis and is a life-threatening emergency. It can affect the whole body, including your breathing, within minutes. Insect stings, certain foods, and drugs such as penicillin are some of the more common causes of severe allergic reactions.

What are the symptoms?

The symptoms of an allergic reaction depend on the type and severity of the reaction. Common symptoms of an allergy are:

  • sneezing
  • itchy, watery eyes
  • stuffy or runny nose
  • itching
  • swelling--for example, swelling of the eyelids
  • a rash or hives (raised, red, itchy areas on the skin)
  • stomach cramps
  • diarrhea.

Some of the symptoms of a severe allergic reaction are:

  • trouble breathing, including wheezing
  • swelling of the lips, tongue, or throat
  • hives
  • pale, cool, damp skin
  • drowsiness, confusion, or loss of consciousness.
  • nausea and vomiting.

How are they diagnosed?

Your healthcare provider will ask about your history of symptoms and examine you.

You may have tests to find out what you are allergic to. For most people the best tests are skin scratch or prick tests. For these tests tiny amounts of suspected allergens are put under your skin. Your provider then looks for reactions to the allergens. In some cases blood tests may help find what you are allergic to.

To identify a food allergy, your provider may suggest that you not eat certain foods for a while. Then you can add each food back to your diet, one at a time. You can then see which foods cause your symptoms to come back.

How are they treated?

Depending on the type of allergy you have and your symptoms, your healthcare provider may prescribe:

  • decongestants
  • antihistamines
  • steroid medicine.

Using a steroid for a long time can have serious side effects. Take steroid medicine exactly as your healthcare provider prescribes. Don’t take more or less of it than prescribed by your provider and don’t take it longer than prescribed. Don’t stop taking a steroid without your provider's approval. You may have to lower your dosage slowly before stopping it.

To treat or prevent breathing problems, your provider may prescribe:

  • an inhaled bronchodilator
  • other types of pills or inhaled medicine.

Mild symptoms may not need treatment.

In some cases, your provider may suggest allergy shots. Shots may be recommended if your allergy symptoms cannot be controlled with medicine, especially if your allergies are severe. A mixture is prepared that contains the allergens found with your allergy tests. The mixture is injected into your skin in tiny but increasing amounts over the course of many months. Over time, the shots make you less sensitive to the allergens. Usually after 4 to 6 months of allergy shots you will start to have relief from your symptoms. You may need to keep getting the shots for 2 years or longer.

If you have severe allergies, your provider may prescribe an epinephrine emergency kit, such as EpiPen or Twinject. You will need to always carry the kit with you. It contains a ready-to-use syringe of epinephrine. If you have a severe allergic reaction, a shot of this medicine can counteract allergy symptoms for a short while until you get medical care. You or someone with you can give you the shot. The kit is not intended as the sole treatment of an allergic reaction. Rather, it "buys" time while you wait for or get to emergency help.

If you have a severe allergic reaction, call 911 right away. Use the epinephrine emergency kit if you have one. Teach family members and coworkers how to help you if you have a severe reaction.

How long will the effects last?

Allergies last different amounts of time from person to person. Some people outgrow their allergies. Others have allergies all their life.

How can I take care of myself?

  • Follow your healthcare provider's instructions.
  • Try to avoid the things you are allergic to.
  • If you tend to have severe allergy reactions, ask your provider about carrying emergency medicine, such as epinephrine. Wear an ID, such as a Medic Alert bracelet, that lists your severe allergies.

How can I help prevent allergies?

There is no known way to prevent allergies. However, some research has shown that breast-fed babies may be less likely than bottle-fed babies to have allergies or asthma.

If your family has a very strong history of allergies, you might try to avoid your family's most common allergens. For example, you may need to stay away from cats. This might keep you from becoming allergic to cats.

Cigarette smoke can make hay fever and asthma symptoms worse. You can help your symptoms by not smoking. It also helps to avoid being around others who are smoking. Children living in homes with smokers are more likely to have asthma.

Where can I get more information?

Many organizations provide support and information for people with allergies and asthma. Here are a few:

  • The American Academy of Allergy, Asthma & Immunology provides educational materials, pollen count reports and maps, and a physician referral directory. Phone: 800-822-2762. Web site:
  • The Asthma and Allergy Foundation of America offers educational programs and services. They also offer asthma and allergy support groups across the country for adults, parents, teens, and caregivers. Phone: 800-727-8462. Web site:
  • The American Lung Association offers educational materials and support group information. Check your local telephone listings for a chapter near you.
  • The Food Allergy & Anaphylaxis Network is a worldwide network that provides educational materials, allergy alerts, and research studies related to food allergies. Phone: 800-929-4040. Web site:

For more information about local support groups in your community, contact your healthcare provider or local hospital.

Developed by RelayHealth.
Published by RelayHealth.
Last modified: 2011-04-13
Last reviewed: 2010-08-02
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
© 2011 RelayHealth and/or its affiliates. All rights reserved.
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