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 intolerances
One 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.