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By Diane M. Yoakam R.N., M.S.N., C.E.N., HealthAtoZ contributing writer

Test your allergy IQ and then learn about asthma.

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Frequently asked questions about allergies

What is an allergy?

An allergy occurs when the immune system becomes hypersensitive and reacts to substances called allergens. Allergens can be a variety of substances including but not limited to pollen, dust, animal dander, molds, chemicals, food and medications. Normally the immune system works to defend the body against harmful invaders. In most allergic reactions, the immune system is responding to a false alarm. The body misidentifies an otherwise harmless substance, and starts a chain reaction that results in what is often called an allergy attack.

What happens within the body during an allergic response?

When an allergic person first comes into contact with an allergen, their immune system starts to make large amounts of a type of antibody called immunoglobulin. At first immunoglobulin G is formed, but over repeat exposures (usually three seasons for perennial allergies), immunoglobulin E, or IgE, is produced. Each IgE antibody is specific for one allergen. The IgE molecules attach themselves to the body's mast cells, which are tissue cells, and to basophils, which are blood cells. When the allergen again encounters the IgE, it attaches to the antibody like a key fitting into a lock, signaling the cell to which the IgE has become attached to release powerful chemicals like histamine, prostaglandins and leukotrienes. These chemicals then travel to various body parts, producing the symptoms of allergy.

What are the symptoms of an allergy and how do they differ from those of a cold?

Common allergy symptoms include:

• Itching of the nose, mouth, eyes, throat and skin
• Runny nose (rhinitis)
• Sneezing
• Nasal congestion
• Tearing
• Scratchy throat
• Impaired smell
• Coughing
• Headache
• Wheezing and shortness of breath

Cold symptoms may be similar to those of an allergy, some distinguishing features of colds and allergies include:

• If all of your symptoms come on at once, it's probably a cold. Allergy symptoms often develop one at a time, maybe with a runny nose first and then nasal congestion days later.
• If you have a sore throat, it's more likely a cold. Allergies may cause itchiness or scratchiness, but they don't usually result in a sore throat.
• If your nose itches, it's probably an allergy, especially if the symptoms get better when you take antihistamines.
• If your symptoms can be linked to a particular exposure (someone's cat) or a particular time of year (early spring), it is most likely an allergy.

What are the most common allergens?

Hay fever. Hay fever is also called allergic rhinitis and involves an allergic reaction to pollen. The pollens that cause hay fever vary from person to person and from region to region. Many trees, grasses and weeds produce extremely small, light, dry, protein particles called pollen. Pollen is spread by the wind. It lodges in the mucus membranes of the nose and respiratory tract, where it stimulates an allergic reaction in a sensitive person. Estimates say 20 percent of the population suffers from some form of hay fever. Your genetic makeup predisposes you to develop this allergic reaction, and reactions may occur at any age.

Here is a guide to which pollens are around at specific times:

• Tree pollens - come first, from March until June
• Grass pollens - peak at the end of May to mid-July
• Weed pollens - most problems with these occur in late August and September

Of all the allergy sufferers in the U.S., 75 percent have allergies to ragweed, 50 percent are allergic to grasses and 10 percent to trees.

Dust allergy. Allergy to dust found in houses is the most common cause of "perennial allergic rhinitis," which simply means that the offending allergens are present year round. House dust isn't a single substance, but rather a mixture of potentially allergic particles. It may contain fibers from various fabrics, cotton lint, feathers, and other stuffing material. Dust often contains microscopic mites, which live in bedding, furniture, and carpets. It is the waste products of these mites that set off the allergic reaction.

It's impossible to totally eliminate dust or dust mites but there are ways to lessen and control the amount of dust in your home:

• Reduce the number of dust-gathering items (or keep them in display cabinets).
• Damp dust when you are cleaning surfaces, as dry dusting often puts particles back into the air.
• Change vacuum filter bags frequently and use double thickness "allergy bags" or use a vacuum cleaner with a HEPA filter.
• Wash bedding materials and window dressings in hot water at temperatures above 130 degrees F to kill dust mites.
• Cover mattresses and pillows with special micro-porous covers, which provide a barrier to mites.
• Limit the number of stuffed animals and don't allow an allergic child to sleep with them.
• Use products such as air filters, ionizers and dehumidifiers to decrease humidity below 50 percent; this may reduce allergy symptoms.

Animal allergy. Household pets are the main cause of allergic reactions to animals. Cats are the main culprit. Pet allergies aren't caused by fur but rather by the proteins in animal saliva, dander and urine. Animals, especially cats, can carry the allergen on their dander. Guinea pigs and gerbils are more popular these days as pets, but they can also cause allergic reactions in some people.

Allergy to pets may take years to develop and the symptoms may persist even after you no longer have the pet. Also, allergens from pets can stay in a home for months after the pet is removed. If you have pet allergies, check with your landlord or the previous homeowners to see if pets lived in your home.

How can I know for sure if I have allergies?

People with allergic symptoms often believe that they have a cold. But it's a cold that seems to last and last. See a doctor if your symptoms continue. The doctor asks you for a detailed medical history of your symptoms. Your history, along with a physical examination, will most likely be the basis for treating your allergies. There are specialists whose practice is solely devoted to allergies. Many primary doctors also treat allergies, since they are such a common complaint.

Skin testing may be recommended for some patients to find the specific allergen responsible for your allergy. In this method, a tiny amount of an allergen is scratched into the skin. If the patient develops a raised welt-like reddened area at the injection site, the doctor has valuable clues as to how to treat the allergy.

What treatments are available for people suffering with allergies?

The goal of all allergy treatments is to reduce symptoms. The following approaches to treatment are most often used:

Avoidance. There's no known way to prevent hay fever, so treatment of this allergy aims to minimize exposure to the offending allergens. Helpful hints for reducing pollen exposure include:

• Don't mow the lawn, and stay inside while someone else is mowing it.
• Keep windows closed as much as possible, especially in the bedroom.
• Drive with your car windows closed.
• Check pollen counts (1-800-9-POLLEN) and try to avoid going outside when they are high.
• Use air conditioners in the home and car to prevent pollen from entering as much as possible.
• Exercise indoors whenever possible.

Medication. Since many allergens can't adequately be avoided, treatment is aimed at reducing the symptoms with medication. Commonly prescribed medications include:

• Antihistamines. These drugs work by countering the effects of histamine, a chemical released by the mast cells that contributes to allergy symptoms. Antihistamines work by relieving sneezing and itching in the nose, throat, and eyes, and by reducing nasal drainage. One common side effect of the over-the-counter antihistamines is that they cause drowsiness. This drowsiness can be severe enough to interfere with your coordination. Sedating antihistamines should not be taken if you are driving or operating machinery. A group of non-sedating antihistamines are available by prescription, including Clarinex®, Zyrtec® and Allegra®.

  Cortisone nasal sprays. Topical nasal sprays, unlike oral or injectable steroids, can provide relief from hay fever symptoms without causing the systemic side effects sometimes associated with steroid use. They reduce the number of mast cells in the nose and they reduce mucus secretion and swelling. Topical nasal sprays are anti-inflammatory drugs that stop the allergic reaction. Unlike antihistamines, nasal cortisone sprays may take several days to begin working and they must be used on a regularly daily basis before and during an allergy season, NOT just as needed. Nasal sprays are often prescribed in combination with antihistamines. Some commonly prescribed cortisone nasal sprays include Beconase®, Vancenase® and Nasacort AQ®, Nasonex®, Rhonocort Aqua® and Flonase®.

  Decongestants. These drugs also help control the symptoms but not the causes of allergies. Decongestants shrink swollen membranes in the nose, making it easier to breathe. They can either be given orally or by nasal spray. Be careful with nasal sprays. They should be used under a doctor's advice for short periods (three to five days), since long-term usage can actually worsen symptoms. Common oral decongestants include sudafed and phenylephrine hydochloride.

  Allergy desensitization or immunotherapy. This type of treatment is often offered to people with more significant allergies, intolerance to medications or multiple target organs. Allergy immunotherapy stimulates the immune system with gradually increasing doses of the substances to which the person is allergic. This type of treatment usually takes six months to a year to become effective and the injections may be required for three to five years. Allergy shots must be managed by a doctor. In very rare instances, severe reactions to the injection can occur. Desensitization has proven to work well in pollen allergies, with success rates as high as 80 percent.

When does an allergy become asthma?

Some people with allergies develop asthma. Symptoms of asthma include shortness of breath, coughing with or without mucus production and wheezing. These symptoms result from a narrowing of the bronchial tubes in the lungs. Shortness of breath and wheezing indicate the need for prompt medical attention. If you have these symptoms during what you believe is an allergy attack, get help right away. Asthma is a serious disease that remains undetected in too many people. Each year many people who were never aware that they had the disease die from complications of an acute asthma attack.

External Sources American Academy of Allergy, Asthma and Immunology Asthma and Allergy Foundation of America

This article was reviewed and updated June 2007.