What You Should Know About
Allergy
The human immune system is designed to quickly mount a powerful, coordinated defense against germs and other potentially damaging foreign substances that attempt to enter the body. To serve this function accurately, the immune system learns to recognize which substances are indeed threatening and which are harmless. However, for reasons we don't yet completely understand, sometimes this process goes awry. In other words, sometimes the immune system mistakenly reacts to a harmless substance as though it were dangerous. When that happens, the person is said to have an allergy.
One of the most common examples of an allergy is hay fever, in which the immune system reacts to plant pollen as though it were dangerous. The congestion, runny nose, and itchy, watery eyes that result are actually produced by the body's needless attempt to remove the pollen - technically called an allergen - from the nasal passages. Many substances can function as allergens; common respiratory allergens include pollens, mold spores, house dust mites, cockroaches, and animal dander.
Allergies can cause many different kinds of symptoms depending on the organ system involved and the severity of the reaction. Besides the respiratory system, allergies commonly affect the skin and may cause hives or eczema. Allergies that affect the digestive tract may cause abdominal cramps, nausea, vomiting, or diarrhea. Sometimes the symptoms begin immediately after exposure to an allergen, but sometimes they can take hours or days to develop.
Diagnosing allergy
An allergy isn't the same as sensitivity to, intolerance of, or a bad reaction to a food or other substance. By definition, an allergy must involve the immune system. Thus, to confidently diagnose an allergy, your doctor will most likely test the reaction of your immune system to certain substances known to be common allergens. |
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First, the doctor will carefully question you about your symptoms, home environment, work, hobbies, and any other pursuits in which you could be exposed to allergens. Based on your answers to those questions, if your doctor still thinks you may have an allergy, you may undergo skin tests to help determine which substances could be causing your allergy symptoms. If necessary, you may need a blood test as well.
Prick test
The prick method is the most common type of skin test. It's safe and causes almost no discomfort. A drop of allergen extract is placed on your skin - usually on your back - and a needle is passed through the extract to make a tiny puncture in your skin. That way, a miniscule amount of the allergen gets just under your skin. If your body has an allergic reaction to that substance, you'll develop a hive at that site within about 15 minutes. Test substances can be placed about 2 inches apart across your back, so your doctor may want to test your body's reaction to several substances at once.
Intradermal test
The intradermal test is another type of skin test. In this one, the doctor or nurse will use a syringe to inject allergen extract into the top layer of skin, which raises a small bubble on the surface. As in the prick test, a hive will appear at the site in about 15 minutes if you're allergic to the injected substance. Intradermal tests are usually done on the upper arm, so fewer allergens can be tested at once. However, this method is much more sensitive than the prick method - so sensitive, in fact, that it can show a reaction to substances that don't actually cause you any symptoms.
Patch test
A third kind of skin test, called a patch test, can be used to look for substances that might be causing a skin reaction called contact dermatitis. To perform the test, the doctor or nurse will place a bit of the suspected substance, such as a cosmetic, on the skin and cover it with a bandage. If the skin is red and peeling under the bandage after 48 hours, you probably are allergic to that substance.
RAST test
The radioallergosorbent (RAST) test is a blood test done in a laboratory. It can be used instead of skin tests to detect allergies. It probably is no more accurate than skin tests, but it may be helpful if you have a skin condition that makes skin testing impossible. This blood test is also the best choice if the doctor thinks you could be severely allergic to the tested substance.
Keep in mind that skin and RAST tests can help to narrow the list of suspected allergens, but they may not give a definitive answer to what's causing your symptoms. Only in light of a detailed description of your symptoms and when they occur will your doctor be best able to make sense of the tests and start you on a treatment program.
Treatment and tips
An allergy can't be cured with a medication in the way an infection can be cured with an antibiotic. That's why it's helpful for you to take steps to avoid the substances that cause your allergy symptoms. (For some ideas, see Rhinitis and Asthma.) Also, your doctor may prescribe one or more medications designed to help control your allergic symptoms.
Where to Get Additional Information
For more information, try these online resources.
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