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What Are Allergies?

Allergies are abnormal immune system reactions to things that are typically harmless to most people. When you're allergic to something, your immune system mistakenly believes that this substance is harmful to your body. (Substances that cause allergic reactions — such as certain foods, dust, plant pollen, or medicines — are known as allergens.)

What Happens in Allergies?

In an attempt to protect the body, the immune system produces IgE antibodies to that allergen. Those antibodies then cause certain cells in the body to release chemicals into the bloodstream, one of which is histamine (pronounced: HIS-tuh-meen).

The histamine then acts on the eyes, nose, throat, lungs, skin, or gastrointestinal tract and causes the symptoms of the allergic reaction. Future exposure to that same allergen will trigger this antibody response again. This means that every time you come into contact with that allergen, you'll have some form of allergy symptoms.

What Are the Signs and Symptoms of Allergies?

Allergic reactions can be mild, like a runny nose, or they can be serious, like difficulty breathing (especially if you have a history of asthma).

Some types of allergies cause multiple symptoms. And in rare cases, an allergic reaction can become very severe — this is called anaphylaxis (pronounced: an-uh-fuh-LAK-sis). Signs of anaphylaxis include trouble breathing or swallowing; swelling of the lips, tongue, and throat or other parts of the body; and dizziness or loss of consciousness.

Anaphylaxis usually happens minutes after exposure to a trigger, such as a peanut, but some reactions can be delayed by as long as 4 hours. Luckily, anaphylactic reactions don't happen often and can be treated successfully.

What Causes Allergies?

The tendency to develop allergies is often hereditary, which means it can be passed down through your genes. However, just because a parent or sibling has allergies doesn't mean you will definitely get them, too. A person usually doesn't inherit a particular allergy, just the likelihood of having allergies.

What Things Are People Allergic to?

Some of the most common allergens are:

Airborne particles. Often called environmental allergens, these are the most common allergens. Airborne particles that can cause allergies include dust mites (tiny bugs that live in house dust); mold spores; animal dander (flakes of scaly, dried skin) and dried saliva from your pets; and pollen from grass, ragweed, and trees.

Foods.Food allergies are most common in babies and may go away as people get older. Although some food allergies can be serious, many just cause annoying symptoms like an itchy rash, a tingly tongue, and diarrhea. The most common food allergies are: milk and other dairy products, eggs, wheat, soy, peanuts and tree nuts, and seafood.

Insect stings. The venom (poison) in& insect stings can cause allergic reactions, and can be severe and even cause an anaphylactic reaction in some people.

Medicines. Antibiotics — medicines used to treat infections — are the most common type of medicines that cause allergic reactions. Many other medicines, including over-the-counter medications (those you can buy without a prescription), also can cause allergic reactions.

Chemicals. Some cosmetics or laundry detergents can make people break out in hives. Usually, this is because someone has a reaction to the chemicals in these products, though it may not always be an allergic reaction. Dyes, household cleaners, and pesticides used on lawns or plants also can cause allergic reactions in some people.

How Are Allergies Diagnosed?

If your family doctor suspects you might have an allergy, he or she might refer you to an allergist (a doctor who specializes in allergy treatment) for further testing.

The allergist will ask you about your own allergy symptoms (such as how often they happen and when) and about whether any family members have allergies. The allergist also will do testing to confirm an allergy. The tests will depend on the type of allergy suspected, and may include a skin test or blood test.

How Are Allergies Treated?

There's no cure for allergies, but symptoms can be managed.

The best way to avoid allergic reactions is to stay away from the substances that cause them — called avoidance. Doctors can also treat some allergies using medicines and allergy shots.


In some cases, as with food allergies, avoiding the allergen is a life-saving necessity. Unlike allergies that can be treated with shots or medicines, the only way to treat food allergies is to avoid the allergen entirely. For example, people who are allergic to peanuts should avoid not only peanuts, but also any food that might contain even tiny traces of them.

Avoidance can help protect people against non-food or chemical allergens, too. In fact, for some people, eliminating exposure to an allergen is enough to prevent allergy symptoms and they don't need to take medicines or go through other allergy treatments.

To help you avoid airborne allergens:

  • Keep family pets out of certain rooms, like your bedroom, and bathe them if necessary. (But for some people with serious symptoms, keeping a pet might not be possible.)
  • Remove carpets or rugs from your room (hard floor surfaces don't collect dust as much as carpets do).
  • Don't hang heavy drapes, and get rid of other items that let dust build up.
  • Clean often (if your allergy is severe, you may be able to get someone else to do your dirty work!)
  • Use special covers to seal pillows and mattresses if you're allergic to dust mites.
  • If you're allergic to pollen, keep windows closed when pollen season is at its peak, change your clothing after being outdoors, and don't mow lawns.
  • If you're allergic to mold, avoid damp areas, such as basements, and keep bathrooms and other mold-prone areas clean and dry.


Medicines (usually pills or nasal sprays) are often used to treat allergies. Although they can control the allergy symptoms (such as sneezing, headaches, or a stuffy nose), they're not a cure and can't make the tendency to have allergic reactions go away.

Many effective medicines are available to treat common allergies, and your doctor can help you to identify those that work for you.

Another type of medicine that some severely allergic people will need to have on hand is a shot of epinephrine (pronounced: eh-puh-NEH-frin). This fast-acting medicine can help offset an anaphylactic reaction. It comes in an easy-to-carry container that looks like a large pen. Epinephrine is available by prescription only. If you have a severe allergy and your doctor thinks you should carry it, he or she will give you instructions on how to use it.

Allergy Shots

Allergy shots are also referred to as allergen immunotherapy. By getting injections of small amounts of an allergen, a person's body slowly develops non-allergen antibodies and has other immune system changes that help ease the reaction to that allergen.

Immunotherapy is only recommended for specific allergies, such as to things a person can breathe in (like pollen, pet dander, or dust mites) or insect allergies. Immunotherapy doesn't help with some allergies, like food allergies.

Although many people find the thought of allergy shots unsettling, shots can be very effective — and it doesn't take long to get used to them. Often, the longer someone gets allergy shots, the more they help the body build up antibodies that fight the allergies. Although the shots don't cure allergies, they do tend to raise a person's tolerance when exposed to the allergen, which means fewer or less serious symptoms.

If you're severely allergic to bites and stings, talk to a doctor about getting venom immunotherapy (shots) from an allergist.

Is It a Cold or Allergies?

If the spring and summer seasons leave you sneezing and wheezing, you might have allergies. Colds, on the other hand, are more likely to happen at any time (though they're more common in the colder months).

Colds and allergies have similar symptoms, but colds usually last only a week or so. And although both may cause your nose and eyes to itch, colds and other viral infections can also cause a fever, aches and pains, and colored mucus. Cold symptoms often get worse as the days go on and then gradually improve, but allergies begin immediately after exposure to the offending allergen and last as long as that exposure continues.

If you're not sure whether your symptoms are caused by allergies or a cold, talk with your doctor.

Dealing With Allergies

So once you know you have allergies, how do you deal with them? First, try to avoid things you're allergic to!

  • If you have a food allergy, avoid foods that trigger symptoms and read food labels to make sure you're not eating even tiny amounts of allergens.
  • If you have an environmental allergy, keep your house clean of dust and pet dander and watch the weather for days when pollen is high. Switching to perfume-free and dye-free detergents, cosmetics, and beauty products (you may see non-allergenic ingredients listed as hypoallergenic on product labels) also can help.

If you're taking medicine, follow the directions carefully and make sure your regular doctor is aware of anything an allergist gives you (like shots or prescriptions). If you have a severe allergy, consider wearing a medical emergency ID (such as a MedicAlert bracelet), which will explain your allergy and who to contact in case of an emergency.

If you've been diagnosed with allergies, you have a lot of company. And the good news is that doctors and scientists are working to better understand allergies, to improve treatments, and to possibly prevent allergies altogether.

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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.

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