Allergy Encyclopedia

Achoo! Do you suffer from allergies? You’re not alone: "Some 50 million Americans have allergies, and that number is on the increase," says Montefiore Medical Center’s Waleed Abuzeid, MD, an assistant professor at the Albert Einstein College of Medicine in New York City.

According to the American Academy of Allergy, Asthma & Immunology (AAAAI), allergies have been on the rise for more than 50 years. (While the reason why remains underdetermined, research makes a strong case for the “Hygiene Hypothesis” explained below.)

The AAAAI also notes that allergic rhinitis or hay fever, a leading cause of allergies, afflicts some 7.8 percent of U.S. adults. And an estimated 15 million Americans, including 1 in every 13 children, have food allergies, some of which can be deadly.

"Allergies are the fifth leading chronic disease in the United States, and the cost of treating these allergies is $15 billion annually,” Abuzeid points out.

If you’re affected by allergies, or unsure about the various terms that get tossed about when the talk turns to allergies, here’s a quick guide to help you understand more.

Allergens: Substances that can cause allergies, including indoor culprits like dust mite and cockroach droppings, and outdoor ones such as pollen and molds. Allergens cause the immune system of an allergic person to overreact and produce allergic antibodies, which trigger the release of chemicals that cause allergic reactions. These chemicals (for example, histamines) cause symptoms like sneezing, stuffiness, and a runny nose in allergic individuals.

Allergic rhinitis: If you’ve got a runny nose, and you’re sneezing and congested, you may have allergic rhinitis. It’s caused by allergens, which are harmless to many but cause a reaction in susceptible people. The condition is either seasonal (hay fever, caused by the pollen from trees, grasses, and weeds) or perennial (year-round, and triggered by allergens like pet dander and dust mites.)

Long-term treatment with allergen immunotherapy, or allergy shots, can bring long-lasting relief from symptoms, and decrease a person’s sensitivity to the allergens.

Anaphylaxis: An extremely aggressive, life-threatening allergic reaction that occurs when the immune system overreacts to an allergen like a bee sting, latex, or medication, causing symptoms such as an itchy rash, lightheadedness, and even trouble breathing and swelling of the tongue. A person must receive emergency medical treatment, including an injection of epinephrine (adrenaline), or anaphylaxis can be fatal.

Antihistamines: Capsules, liquids, pills, and chewable tablets that block the action of the chemical histamine. Histamine can cause the runny noses, sneezing, swelling of the nasal passages, congestion, and itchy, runny eyes associated with allergies; antihistamines treat these symptoms.

Challenge test: If a food allergy is suspected, your physician may have you consume a tiny quantity of the food in the office. "It’s done in a supervised environment with a physician or someone who could treat a reaction such as anaphylaxis if it occurs," Abuzeid explains. For example, in a peanut butter challenge test, you would eat a small amount of peanut butter under your doctor’s supervision. If you then developed hives, you would be given an antihistamine and observed to see if any other symptoms occur.

Corticosteroids: Not the same steroids used by some athletes, these medications are ingested via inhaler and used to treat some asthma and certain allergic conditions, like allergic rhinitis. Considered the most effective long-term medicine for asthma, corticosteroids need to be taken consistently in order to prevent asthma flare-ups.

Dander: The tiny flecks of skin shed by dogs, cats, birds, and other animals with feathers or fur, dander can cause an allergic reaction in susceptible individuals. Dander isn’t the only pet allergen that can be a problem: proteins found in pet saliva and waste can also cause allergic reactions.

Decongestants: These over-the-counter nasal sprays can be helpful in treating allergic rhinitis, but prolonged use can actually cause rebound congestion of the nasal membranes, and users can become dependent on them. Dependence can last for months or even years.

"You don’t want to use them for more than five days since they can start to cause damage to the nasal mucosa or lining," Abuzeid warns. "People who take decongestants feel that they can breathe better, but decongestants start to alter the way the receptors in your nose work, and they can also reduce the amount of natural ‘decongesting’ chemicals released by your nasal lining. The end result is increased swelling and dilation of the nasal lining, which can cause symptoms of severe congestion."

Hygiene Hypothesis: The theory that the rise in the number of people with allergies is a result of the world being “too clean.” As children, we are no longer exposed to germs or other agents that were common in generations past. As a result, like an unused muscle or skill, our immune systems have become less effective, and are not as adept at distinguishing between infectious agents (like bacteria) and harmless irritants (like pollen).

Pollen: These seed-like plant cells, or spores, are a common trigger of allergic rhinitis. People with allergies should pay attention to the pollen count, or the amount of pollen in the air. To determine the pollen count, a pollen counting station, typically situated on a rooftop, collects tree, grass, weed, and mold spores over a 24-hour period. Then the station is moved to a lab, where the spores are analyzed for both pollen type and concentration. On days when the pollen count is known to be high, allergy sufferers are usually advised to start their hay fever medications right away—before their symptoms worsen.

Skin test: A relatively safe way of determining if an individual has a non-food allergy, a skin test involves administering a diluted concentration of a suspected allergen into the skin. “If the person is allergic, there can be a localized reaction, but it’s much safer to do a skin test because the risk of anaphylaxis is low,” Abuzeid explains.

Waleed Abuzeid, MD, reviewed this article.


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