Your immune system protects your body from potentially dangerous invaders. Allergic reactions are a type of immune response and are determined by the interplay of many factors, including your genes, your environment, what you’ve been exposed to and how well your immune system normally works. The tendency to develop allergies runs in families—if you have an allergic parent, there’s a good chance you’ll also be allergic, though not necessarily to the same things. You can be allergic to one or two things or to many related or unrelated things.
Most allergies begin in early childhood, and early environmental factors play a major role in their development. But allergies can appear at any age and can also go away for a few years—or for good. Unpredictable is the word.
Allergies: an overzealous immune system
An allergic reaction occurs when your immune system mistakes a normally harmless substance for a dangerous invader and produces a needless inflammatory response. This involves the creation of antibodies, specific proteins designed to battle harmful entities.
Allergic reactions can be caused by countless “foreign” (or “nonself”) substances that you inhale or consume or that come in contact with your skin or mucous membranes. These are called allergens and are typically proteins. They are found in pollen, mold spores, animal dander (skin flakes), debris from dust mites and cockroaches, foods (such as peanuts or eggs), insect venom, some medications and many other sources.
Exposure to an allergen is not a problem unless you have been sensitized to it—that is, were exposed to it previously. It may take months or years of repeated exposure before full-blown allergic symptoms develop.
The immune response involves a veritable alphabet soup of white blood cells (key components of the immune system). T-cells recognize the allergen as foreign and instruct B-cells to produce special antibodies belonging to the immunoglobulin E (IgE) class. Each type of IgE antibody fits a specific allergen. Some of these antibodies bind to mast cells, which are scattered throughout the skin, respiratory tract, lining of the digestive tract and elsewhere in the body.
Eventually, when you come in contact with the allergen again it attaches to the antibodies bound to the mast cells. The mast cells release chemicals—notably histamine, leukotrienes and prostaglandins— that set off a chain reaction that inflames the mucous membranes and brings on the classic allergy symptoms. Histamine is one of the key players in inflammatory reactions, which involve, for instance, small blood vessels that dilate and tissues that become red and swollen. Symptoms include itchy, inflamed skin and eyes, sneezing, constriction of bronchial tubes and chest tightness. Increased mucus production in the nasal cavity and airways results in runny nose, postnasal drip and coughing.
Exposure to allergens at times when your body’s defenses are weak, such as after an illness, may increase your risk of developing allergies.
Different allergy reactions
Though there are general patterns, people vary in the severity and kinds of reactions they have to allergens. In addition, there are different types of allergic reactions, depending in part on the organs involved. The most common symptoms affect the nose, sinuses, lungs, eyes, skin and digestive system. Allergic conditions include hay fever, allergic asthma, hives and eczema (atopic dermatitis). Symptoms may appear shortly after exposure to an allergen, or can take several hours (particularly if it is food-related). In rare cases, reactions occur after 24 hours.
The worst case scenario is anaphylaxis, a severe and potentially life-threatening reaction to allergens such as insect venom, peanuts, tree nuts, eggs, milk, fish, shellfish, soy, medication (especially penicillin) and latex. Caused by a massive release of inflammatory compounds by mast cells, the reaction usually comes on in five to 30 minutes, but sometimes several hours later.
Symptoms of anaphylaxis can be subtle at first, like tingling in the mouth or a warm feeling over your face or body, followed by serious symptoms such as wheezing, difficulty breathing, swelling of the lips, throat and tongue, dizziness or lightheadedness (caused by low blood pressure), hives, and possibly cramps, diarrhea or vomiting. The severity of an attack does not predict the severity of subsequent attacks. In the most severe cases, the larynx swells and the bronchial tubes go into spasm, which can cut off breathing; blood pressure can plummet to dangerously low levels.
If you have an anaphylactic attack, you need an immediate injection of epinephrine. Call 911 immediately. Don’t wait to see if your symptoms go away or get better on their own.
If you’ve ever had an attack, you must always carry a penlike auto-injector (such as EpiPen or Auvi-Q) so you can give yourself an injection of epinephrine whenever needed. You should wear a medical bracelet or necklace that lists your allergies (or list them in the “in case of emergency” info on your cell phone) so that health care providers and others will know about your condition if you are unconscious. Teach your family and friends how to help you if you have anaphylaxis, since you may not be able to help yourself. If you have a personal or family history of anaphylaxis, you should be evaluated by an allergist.
Allergies: getting diagnosed
It’s often clear what has caused an allergic reaction—say, your arm swells up and itches after an insect sting. But many times the culprit is not obvious. In that case, diagnosis is based on your personal information (exposure history, symptoms, history of allergies and conditions that often accompany allergies), family history of allergic disorders, a physical exam, skin tests and sometimes blood tests. Your regular health care provider can treat most allergy problems, but may refer you to a board-certified allergist.
The goal is not merely to treat your symptoms when they occur, but also to identify the cause of your allergies and find ways to either prevent your allergic response or minimize the risk of reactions.
Note: If you were diagnosed with an allergy (especially to a food) years ago, consider being checked again. Your allergy may have subsided, or you may have been misdiagnosed, based on outdated tests.
Skin or blood tests are part of a diagnostic workup for allergies, typically done by a board-certified allergist. They can show only that you have been sensitized to a given substance. To confirm an actual allergy, the test results must correlate with your symptoms.
Skin tests. This is the most common method, and there are several ways to do it. With prick tests, a small drop of the suspected allergen (in diluted form) is applied to the skin, a needle is passed through the drop, and the skin is pricked. Intradermal testing involves injecting the diluted allergen just below the surface of the skin. It may be done if the prick test is negative (because intradermal tests are more sensitive). Skin patch testing can be done if you have had an allergic skin reaction, such as to cosmetics or jewelry. The allergen is put on a patch that is applied to the skin for two days.
The allergist will look for a reaction characterized by an itchy raised bump with surrounding redness. For skin prick and intradermal testing, this typically occurs within 20 minutes (but can also be delayed for several hours); for the patch test, the site is checked a few days later.
Skin testing requires a skilled allergist to administer it properly and interpret the results correctly—and to not overdiagnose allergies. There can be false positives due, for example, to cross-reactivity or to impurities in the extracts. Downsides are that you have to stop antihistamines before testing, and your skin has to be rash-free. Though uncommon, you may develop temporary allergy symptoms, such as a runny nose, red eyes and rash; more serious reactions, including anaphylaxis, are rare.
Blood tests. These tests measure levels of IgE antibodies that are produced in response to particular allergens. They are preferable to skin tests if you have a severe skin condition such as psoriasis or are taking medications that can interfere with skin testing; if your allergist suspects you might have a severe reaction to a skin test; or if you have dark skin (which makes interpretation of skin tests harder). Blood testing may also be preferable in infants and young children, who may find this easier to tolerate than multiple skin pricks.
Challenge test. Another way to confirm (or disprove) an allergy is with a challenge test, in which you inhale or consume a small amount of the allergen to see if you have a reaction. Because this test has the potential to cause a serious reaction, it is always done under medical supervision.
Dubious tests. There are many unproven, non-standardized or just downright nonsensical tests that you should avoid, including cytotoxic testing, IgG testing, applied kinesiology, hair analysis, pulse testing, facial thermography and gastric juice analysis. Some claim to find “hidden” allergies. All can lead to overdiagnosis or, worse yet, miss an allergy that can be life-threatening. Not surprisingly, these tests are often done by practitioners who also just happen to have the right “cure” for the allergy supposedly revealed. You should also avoid home allergy tests and allergy testing offered at supermarkets or health fairs.
Immunotherapy for Allergies
Known as immunotherapy or desensitization, allergy shots can be an effective long-term treatment for people who suffer from a variety of allergies, including allergic rhinitis (caused by pollen, dust mites or animal dander), asthma and severe reactions to insect venom, especially when allergens can’t be avoided and medication doesn’t help enough. The treatment gets at the underlying cause of allergies—modifying the immunological response to allergens, with subsequent reduction of the allergic inflammatory reaction—rather than just treating the symptoms. Such shots are not used for food allergies, but oral immunotherapy has had promising results in patients who’ve had severe reactions to food.
Typically once a week over the course of several months, an allergist injects increasing amounts of the purified allergen under your skin to desensitize you, until you reach a maintenance dose, which is typically continued once a month for at least three years. It may take up to 6 to 12 months before you notice a reduction in symptoms. In many people, the beneficial effects last years after treatment has stopped.
“Rush immunotherapy” involves increasing the dose of injected allergens much more quickly so as to “rush” the initial phase of the treatment. Because of the increased risk of an anaphylactic reaction, rush immunotherapy should only be done under close medical supervision.
An attractive alternative to injections for nasal allergies is sublingual immunotherapy via drops or tiny tablets you place under your tongue, allowing them to dissolve and be absorbed through the mucous membranes; doses of the allergens are increased over time. The treatment has long been popular in Europe. Sublingual tablets for grass and ragweed pollen have been approved by the Food and Drug Administration (FDA); some allergists here have been using extracts approved for injection as “off-label” sublingual treatments. Some studies have found that sublingual immunotherapy significantly reduces allergic reactions to pollen and dust mites in adults and children, and also reduces the need for medication.
Published April 17, 2014