What Is An Allergic Reaction: Allergies
Content provided by the Faculty of the Harvard Medical School
What is an allergic reaction?
Clearly, your body’s immune system plays a very important role in your allergies. Allergies belong to a category of immune system responses called hypersensitivity responses. If the immune system is not involved, it is not, medically speaking, an allergy.
People often confuse reactions from irritants in the environment — like a runny nose from cold air, smoke, or perfumes — with a true allergic reaction such as hay fever, which is an immune system response to an allergen such as ragweed. Some people develop an itchy, red rash after contact with certain chemicals such as a harsh laundry detergent, but if the immune system isn’t involved, it is an irritation, not an allergy. Likewise, someone who suffers from bloating and diarrhea after drinking milk or eating dairy products may have an intolerance , not an allergy, to lactose, a natural sugar found in cow’s milk, because they lack the enzymes needed to digest lactose. However, this picture can get murky because some people are, in fact, allergic to one or more of the proteins in milk. This illustrates how tricky it can be to determine a diagnosis and design a treatment.
Tolerating intolerancesOne way of defining intolerance is by saying what it isn’t: It isn’t the result of an overzealous immune system response. Typically it is a response to a chemical or the consequence of an insufficiency of a natural compound. For some people, the caffeine, theobromine, and methylxanthine in tea, coffee, chocolate, and cocoa cause symptoms of acid reflux, jitteriness, or insomnia. The chemicals in red wine can cause migraines in some people; monosodium glutamate (MSG) in Chinese dishes bothers others — although the latter is not as common as people tend to think it is. Other people suffer discomfort from milk products because their bodies produce little or no lactase (the enzyme that breaks down lactose in milk), a condition that can worsen with age. As with allergies, avoidance is the first line of treatment for intolerances. Specific strategies may help alleviate the intolerance. For example, for lactose intolerance, you may be able to boost your lactase levels by taking nonprescription supplements available in retail stores, although the benefits are variable. If you suffer from digestive disturbances, check with your doctor rather than attempting self-diagnosis. |
Appreciating the distinctions among allergies, irritant sensitivities, and intolerances is important to obtaining a correct diagnosis that will lead to the best treatment. Although the treatment is sometimes the same for both an allergy and an irritant response, this is not always the case.
| Last updated: | August 21, 2006 |
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| Reviewed By: | Faculty of Harvard Medical School |
Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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