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.