Key Questions About Allergies

What is an allergy? What are the most common types? How is an allergy diagnosed? Get these answers and more.
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1. What Is an Allergy?
An allergy is the immune system’s excessive sensitivity and over-response to a harmless foreign substance in the body, such as plant pollen, a certain food, a drug or any one of many other substances. Whatever the foreign substance, or “allergen,” the immune system responds as if to a real threat by triggering what is called an immune response, which in these cases is known as an allergic reaction.

2. What Happens During an Allergic Reaction?
In an allergic reaction, the immune system responds to the allergen by producing a highly specific antibody called immunoglobulin E (IgE). While everyone has IgE antibodies, a person who is allergic has an overabundance of them. When the IgE antibodies attack the allergens, they trigger mast cells, or defensive white blood cells, to release histamine and other chemicals that produce the allergic symptoms of inflammation: swelling, mucous production, itching, rash, hives or other symptoms, depending on the type and location of the allergy.

3. Are Allergic Reactions Dangerous?
For most people, allergy symptoms are mild or moderate, but for some hyperallergic people, an allergic reaction can be life-threatening. Anaphylaxis is a runaway allergic reaction that involves the whole body. Anaphylaxis can cause extreme swelling in the lungs and airways that can make breathing or swallowing difficult, as well as severe abdominal pain, cramps, vomiting, diarrhea, and mental confusion or dizziness. Anaphylaxis is a medical emergency requiring immediate treatment.

4. How Common Are Allergies?
As many as 50 million Americans are allergic to something. Allergies are the country’s sixth leading cause of chronic illness, according to the Allergy Report from the American Academy of Allergy, Asthma and Immunology.

The tendency to develop allergies is genetic, though the specific type of allergy does not appear to be inherited. If one or more of your parents has an allergy, you have a high risk of developing an allergy, too. The genetic tendency to produce IgE and allergic reactions in response to ordinary substances is called atopy.

Also, medical experts say that exposure to potential allergens when the body’s defenses are weak, such as after a viral infection or during pregnancy, may contribute to the development of allergies to those substances.

5. What Are the Most Common Allergens?
Allergens are found in indoor and outdoor environments, and may come from plants, food, pets, or even household products. Common allergens include:

Pollen from grass, weeds and/or trees produces hay fever, a common seasonal epidemic.

Dust mites, or microscopic organisms that live in dust and in the fibers of upholstered furniture, rugs, pillows, and mattresses. They are especially prevalent in warm, humid areas. Cockroach allergens are common in urban, inner-city environments.

Mold: These are microscopic fungi that produce airborne spores that enter the body when we breathe. Indoor mold is found in damp areas, such as basements, bathrooms or rooms that have leaks or have been flooded. Mold can also be found outdoors in grass, leaf piles and mulch, or around mushrooms.

Animal dander and proteins: The most common animal allergen is animal dander, which is particles of proteins secreted by glands in the animal’s skin, then shed into the air. Proteins from an animal’s saliva, feces, urine, or feathers also can trigger allergic reactions for some people.

Food components: Common food allergens in Western cultures include shellfish, peanuts and tree nuts. In addition to those, children sometimes are allergic to milk, eggs, soy and wheat.

6. How Are Allergies Diagnosed?
Allergies can be confirmed and identified by skin or blood tests, but they make themselves known by their symptoms. For example, while the symptoms of allergic rhinitis may resemble a cold, you may begin to suspect an allergy if symptoms last longer than a week or two and then tend to recur.

The first step in diagnosis is a medical history to identify a family history of allergies or circumstances that might be exposing the patient to likely allergens. The patient will be asked about the timing of allergic reactions and how long they have been recurring.

For food allergies, elimination diets can be used to systematically eliminate suspected allergens to see if the reactions disappear. To confirm a diagnosis, an allergist may order lab tests or perform tests in the office.

7. What Allergy Tests Might My Doctor Use?
Lab tests an allergist may order during diagnosis may include:

Allergen skin test: In this test, the allergist introduces tiny amounts of an allergen under the patient’s skin with a pin-prick. In an allergic patient, the allergen will produce a swollen itchy patch surrounded by an area of redness. Usually, this office procedure can test for several allergens at the same time.

Radioallergosorbent blood test (RAST): This blood test determines the presence of IgE antibodies in the blood. High levels of these antibodies point to particular allergies. The RAST blood test is not considered as accurate as the allergen skin test.

8. How Are Allergies Treated?
Allergies cannot be cured, so treatment generally involves one or more of the following strategies to control or prevent allergic reactions:

Dust mites: Use sheets, pillowcases and mattress covers that are impermeable to dust mite allergens; regularly wash linens in hot water and vacuum the bed frame weekly.

Cockroaches: Seal cracks in the floor and walls and clean to eliminate food and water sources.

Food allergies: Avoid known food allergens; read packaging to check for ingredients such as peanuts that may have been added; ask restaurant staff about specific ingredients in prepared foods.

Animal allergens: Remove pets from the home to get rid of animal hair and allergens such as dander, saliva and feces.

Pollen: Remain indoors during periods of high pollen counts; wash hands and clothing after being outdoors to remove pollen grains and prevent transferring them to the eyes and nose.

Mitigating symptoms with medication: Both prescription and over-the-counter medications can relieve certain allergy symptoms.

Skin contact allergies, eczema, and allergic conjunctivitis: Treat with topical antihistamines, decongestants, and topical corticosteroids, including ocular forms for use in the eye. In severe cases, systemic corticosteroids may be needed.

Allergen immunotherapy: It is sometimes possible to desensitize a person to a particular allergen using allergen immunotherapy. The patient is given gradually increasing doses of allergens by injection until the immune system learns to tolerate the allergen without producing an allergic reaction. Immunotherapy can reduce or prevent symptoms as well as minimize the severity of allergic exacerbations and keep the disease from getting worse.

Peanut Allergies on the Rise What Every Parent Should Know

As the number of children in the United States who have a peanut allergy or other food allergy continues to rise, more schools are becoming “nut-free.” Even children without peanut allergies are forbidden to bring school lunches or afternoon snacks that have nuts. The reason: fear of setting off serious, even life-threatening reactions in other children with nut allergies.

Indeed, tree nut and peanut allergy are two of the most dangerous types of food allergies. Most people with peanut allergies will have a reaction one of the first times they are exposed. And of all the food allergies, tree nut and peanut allergies are the leading causes of life-threatening anaphylaxis, in which swelling affects the whole body and can obstruct the airways.

The Rise in Peanut Allergies

From 1997 to 2003, the incidence of peanut allergy in children doubled. Why the sharp rise? “At this point in time, we don’t have a clear answer,” says Julie McNairn, MD, an allergist/immunologist in Cincinnati. It might have something to do with the fact that Americans tend to eat dry-roasted peanuts: “There is some suggestion that [during the roasting process], the [peanut] protein is altered, such that it will cause children who eat dry-roasted peanuts to have an allergy, as opposed to someone who eats boiled peanuts,” explains Dr. McNairn.

The number of children with peanut allergies, however, is not the only issue. “The problem is even more than numbers,” says Sami Bahna, MD, a professor of pediatrics and medicine and chief of allergy and immunology at Louisiana State University Health Sciences Center. “The severity of food allergies is going up.” There has also been an increase in severe rashes, intestinal problems, and life-threatening anaphylaxis reactions. “People [with peanut allergies] used to react by eating the food, but there are many people who now react by touching or smelling the food,” says Dr. Bahna.

What’s more, a 2007 study published in the journal Pediatrics found that children are being exposed to peanuts and developing peanut allergies at an earlier age than they were a decade ago. The Duke University Medical Center team that did the study is now investigating whether eating small amounts of peanuts might help children who are prone to allergies mount an appropriate immune response.

Reducing Your Child’s Risk of a Peanut Allergy

In 2000, the American Academy of Pediatrics (AAP) advised pregnant and breastfeeding mothers to avoid eating peanuts to reduce their child’s risk of developing a peanut allergy. They also recommended delaying giving peanuts to children younger than age 3 who are at higher risk of food allergies — for instance, those who have an immediate relative who’s allergic to peanuts. But more recent research now suggests that there is no association between a mother’s intake of peanuts during pregnancy or nursing and her child’s risk of developing a peanut allergy. And the evidence about the best time to introduce peanuts is mixed.

The AAP now says that current evidence does not support peanut restriction during pregnancy or breastfeeding, and that there is no convincing evidence that delaying peanut-containing foods beyond 4 to 6 months of age will reduce the risk of peanut allergy.

Is Cleanliness Among the Causes of Allergies?

Hundreds of ordinary things we come in contact with on a daily basis can trigger allergic reactions and asthma — from pollen and mold to pet hair and dust mites. It’s not an insignificant problem: More than 50 million Americans have some type of allergy, according to the American College of Allergy, Asthma and Immunology, and about 25 million Americans have asthma — a number expected to increase, according to the U.S. Centers for Disease Control and Prevention (CDC).

If someone in your household has allergies or asthma, your first reaction may be to regularly try to remove allergy irritants like these from your home. But all that mopping, sweeping, air freshening, and spray cleaning could actually increase your risk of allergies and asthma. Research has shown young children who aren’t exposed to allergens and germs in their early years face a higher risk of developing asthma and allergies later in life. One study of Amish children who live and work on farms, published in the Journal of Allergy and Clinical Immunology, suggested that early-life exposure to allergens may prevent the immune system from developing allergies. It’s not the first to make such a connection. Additionally, chemical sprays used for cleaning might trigger asthma and allergies in some adults.

Allergy Causes: The Hygiene Hypothesis

The argument that too-clean environments contribute to allergies is called the “hygiene hypothesis.” Generally, the idea is that exposure to germs and infection helps build the immune system, which can protect against allergies and asthma.

Some experts have associated cleanliness with allergies for several years. One study of 900 infants found that children who attend daycare are 35 percent less likely than those who stay home to develop allergies and asthma later in life. The ones who entered daycare between 6 months and 1 year of age had 75 percent less asthma by age 5 than their peers.

“It’s a hypothesis, but it doesn’t explain everything, such as why children raised in inner cities, where they are exposed to allergens like air pollution and cockroaches, have higher rates of asthma,” says Kenneth Rosenman, MD, chief of the division of occupational and environmental medicine at Michigan State University.

Studying Allergies on the Farm

The best data supporting the idea that early exposure to allergens reduces the risk of allergies comes from studies of farms in Europe, says Rosenman. These farm studies, where exposure to animals, dirt, and germs is more or less unavoidable, show that a messy childhood might protect against allergies.

A similar study of 1,300 children in New Zealand showed that children whose mothers lived on farms during pregnancy were 50 percent less likely to have asthma and significantly less likely to have allergies such as hay fever or eczema. Published in the European Respiratory Journal, the study suggests that the exposure of pregnant women to possible allergy causes enables their bodies to create antibodies for the fetus as well.

Cleaning Products and Allergies

Not only does a too-clean environment put children at risk of later asthma and allergies, the act of cleaning might be causing asthma and allergies in adults.

According to a study of more than 3,000 adults who did not have asthma when the study began, using cleaning sprays more than once a week can trigger asthmatic attacks and the risk of asthma increased as the use of sprays increased. Sprays that could lead to asthma and allergies include glass cleaners, furniture cleaners, and air fresheners, the researchers reported in the American Journal of Respiratory and Critical Care Medicine.

Previous studies have shown that people whose work exposes them daily to cleaning products — especially spray de-greasers, bleach solutions, and air fresheners — are more likely to have asthma or the kinds of respiratory symptoms, such as coughing and wheezing, that people associate with allergies. Women who already have some type of lung infection or illness are at increased risk from spray cleaning products. The effect appears to be isolated to spray cleaners. Use of cleaning agents in other forms did not have the same effect.