A patch test looks a little something like this.

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Testing for Allergies in Children

Sometimes children's allergies are all too apparent, and sometimes they're not. If you suspect your child has allergies, you should have them checked out by your family doctor. Breaking out in hives may be the result of any number of things, and medical advice and testing are a good idea when you're dealing with any kind of adverse reaction.

Among kids under age 6, allergies are an issue for about 8 percent of them [source: Asthma and Allergy Foundation of America]. Children who have allergies often have asthma, too -- about four out of five kids with asthma have allergies [source: Asthma and Allergy Foundation of America].

If you think your kid is allergic to something (or many things), your pediatrician will likely recommend an allergist who will collect anecdotal accounts from you, thoroughly examine the child, and test him or her for indications of allergic reaction (chiefly the presence of IgE).

The allergist may check for allergies through a number of different methods. One is an elimination test, for which different foods and possible allergens are removed from the child's environment until symptoms disappear. One by one, the substances are reintroduced into the child's life until one triggers a reaction.

A skin-prick test may be performed, in which skin on the back or arm is pricked with one or more needles that contain traces of specific allergens. The allergist then looks for a raised bump on the site of injection, and the bump's size indicates the degree of allergic reaction. Results aren't always reliable, though, and may produce a false positive or a false negative.

Another allergy test is the RAST test (radioallergosorbent test), during which radioactive markers are introduced to the child's body to check for an IgE reaction. Many other tests are available (such as patch testing), but they're less widely used. Your allergist will help you choose the best for your child's situation. The good news is that by testing different allergens, the allergist may discover more than one that triggers an allergic reaction. That doesn't sound like good news, but if your child has multiple allergies, it's best to discover them in a medical facility and not when you least expect it.

Next, we'll learn about food allergies in particular.