What are allergies?

An allergy is your body’s reaction to a substance that is normally harmless. With allergies, your body sees the substance as harmful or foreign and your immune system reacts to the substance. Substances that can cause an allergic reaction are called allergens. Allergic reactions are common.

What is the cause?

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 sensitive to it. Usually this means your body has to be exposed to the substance at least once. Once it is sensitive to it, your body will react every time you have contact with the substance. Most reactions are mild, but some are life-threatening.

Many things can cause an allergic reaction. Your body may react to an allergen when you breathe, swallow, or touch it. The most common allergens are:

  • Pollen (small particles in the air from grasses, weeds, or trees)
  • Mold
  • Animal dander (dried skin flakes)
  • Dust and dust mites (very tiny bugs)
  • Latex (a liquid from rubber trees that is used in many products, like gloves and toys)
  • Medicines
  • Insect stings and bites
  • Foods, such as shellfish, eggs, milk, tree nuts, and peanuts
  • Chemical irritants, such as nickel, dyes in fabric, or cleaning products
  • Poison oak, poison ivy, or poison sumac (over half of the people in the US are allergic to the oils from these plants)

It is not known why some people develop allergies. You may have an increased risk if other people in your family have allergies.

What are the symptoms?

Allergy symptoms may go away in a few minutes without treatment, or they may last for several days. Common allergy symptoms may include:

  • Sneezing
  • Itchy, watery eyes
  • Stuffy or runny nose
  • Swelling–for example, swelling of the eyelids
  • Itching, a rash, or hives (raised, red, itchy areas on the skin)
  • Stomach pain
  • Diarrhea

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

  • Severe trouble breathing, including wheezing
  • Swelling of the lips, tongue, or throat
  • Hives
  • Pale, cool, damp skin
  • Fast or pounding heartbeat
  • Nausea and vomiting
  • Feeling intense fear that something terrible is about to happen
  • Drowsiness, confusion, or fainting

How are they diagnosed?

Your healthcare provider will ask about your symptoms and medical history and examine you. Most common allergies can be diagnosed from your history and physical exam.

Tests may include:

  • Blood tests
  • A skin prick test, which uses a drop of allergen extract (liquid) put under your skin using a needle
  • Elimination diet, which means you avoid eating certain foods for a few weeks to see if allergy symptoms go away
  • Food challenge test, which is eating food that is a possible allergen to see if you have a reaction. This test is done only by a healthcare provider who is ready to treat you if you have a serious reaction to the food.

How are they treated?

Your treatment will depend on the type of allergy you have and your symptoms. Mild symptoms may not need treatment, but you may need to avoid the known allergen.

Several kinds of medicines may be used to treat allergies:

  • Decongestants reduce swelling in your nose and sinuses. They may also lessen the amount of mucus made by your nose. If you use decongestants more often than directed, your stuffy nose may get worse. Do not give decongestants to children under the age of 4. If your child is between the ages of 4 and 6, ask your healthcare provider before giving decongestants.
  • Antihistamines block the effect of histamine and help reduce your symptoms. Histamine is a chemical your body makes when you have an allergic reaction. Do not give antihistamines to children under the age of 4. If your child is between the ages of 4 and 6, ask your healthcare provider before giving antihistamines.
  • Steroid pills or nasal sprays help reduce the irritation and swelling in your body. By lessening the swelling, you will have fewer symptoms and be able to breathe better. 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.
  • Immunotherapy is a type of treatment that includes shots or pills containing small amounts of the allergens you are allergic to. It may be recommended if your allergy symptoms cannot be controlled with medicine. It may take several months of treatment before your symptoms get better.

A severe allergic reaction is life-threatening and usually needs to be treated with epinephrine. Epinephrine relaxes the muscles in your airways and throughout your body. It is usually given as a shot. You may need more than one shot to decrease your symptoms. If you are known to have a serious reaction, your provider may want you to carry an emergency kit. You or someone with you can give you the shot. Whether or not you have epinephrine, call 911 or your local emergency services right away for all severe allergic reactions.

How can I take care of myself?

Follow the full course of treatment prescribed by your healthcare provider. In addition:

  • Try to avoid the things you are allergic to.
  • Don’t smoke, and stay away from others who are smoking.
  • If you were prescribed an emergency kit, carry it at all times. Use it as directed by your provider. Check the expiration date for the medicine and replace it as needed to make sure it will work.
  • Wear a medical alert bracelet or necklace that warns of your allergy and tells what to do in case of an emergency. Teach family members and coworkers how to help you if you have a severe reaction.
  • Call 911 or your local emergency services for all severe allergic reactions.

Ask your provider:

  • How and when you will hear your test results
  • If there are activities you should avoid and when you can return to your normal activities
  • How to take care of yourself at home
  • What symptoms or problems you should watch for and what to do if you have them

Make sure you know when you should come back for a checkup. Keep all appointments for provider visits or tests.

For more information contact:

How can I help prevent allergies?

There is no sure way to prevent allergies.

If your family has a very strong history of allergies, try to avoid your family’s most common allergens. For example, staying away from dogs or cats might help if several family members are allergic to them.

Developed by RelayHealth.
Adult Advisor 2015.1 published by RelayHealth.
Last modified: 2015-02-02
Last reviewed: 2014-09-18
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.
Copyright ©1986-2015 McKesson Corporation and/or one of its subsidiaries. All rights reserved.

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