Food allergies are a lot harder to pin down than allergies to airborne substances, cosmetics or drugs. Skin tests are little help – physicians sat they’re far less reliable for food than for inhalants such as dust or pollen. And symptoms don’t usually fall into simple, easily observed patterns because of the complex (and not fully understood) what that foods trigger allergy, and because of the motley makeup of our modern diet.

A few people can feel their lips, mouth and throat begin to swell or itch even before the food in question reaches their stomach. More often than not, however, trouble erupts farther along, as food is processed by the digestive system – resulting in anything from nausea and queasiness to gas and diarrhea, plus various difficulties in between.

As food allergens wend their way to the rest of the body, symptoms are no different from those of inhalant energy – wheezing, or skin rashes, or dizziness, or joint pains and so on. These symptoms can take time to develop – a few hours, maybe, or a day or so. Because that time lag, you may have difficulty linking what you ate to how you feel.

Granted, some people – about 1 out 20 – are so sensitive that the smallest nibble of an offending food can spark an immediate, recognize reaction. It you break out in hives each time you eat shrimp, you’ve got an open and shut case of shrimp allergy. But it’s seldom that simple.

Since food takes about four or five days to journey from entrance to exit, most people react later. So you might blame your symptoms on the cheese you ate at lunch, when the real cause is the eggs you ate for breakfast. Or the melon you ate yesterday.

Here’s another variable: do you seem to tolerate a food some times, but not others? You still can allergic to a food even if you don’t react every time you eat it. The problem food may very well be eaten for quite a while, with no symptoms. Then, as antibodies accumulate to a certain threshold, the attack occurs.

One doctor compares this ”allergic threshold” to water filling to rain barrel. All’s well until the water level reaches the brim. Then a tiny drop causes an overflow. By rotating foods, or eating troublesome food only at widely spaced intervals, you can keep most food allergies from reaching that critical point.

How close you to come to going over the edge also depends on how much you eat, and when. Perhaps, you’re only mildly allergic – you may able to get away with one or two strawberries, but eating a pintful is a full scale disaster. Or, since cooking breaks down food to a degree, you may discover, for instance, that you can eat celery cooked, but not raw.

Or your symptoms may appear only if two or more allergic foods are eaten at the same meal – in effect, overwhelming the system. That’s particularly true for closely related foods like beef and milk, or mushrooms and yeast. By the same token, you may react to a food only during pollen season or when suffering from other airborne particles.

Or when you have a cold. Or when drinking alcohol. Or if eaten on an empty stomach. Another interesting twist is that allergic reactions are not always uncomfortable. In fact, you may feel better after eating allergic food. Doctors call the reaction ”allergic addiction,” and compare it to the temporary lift one gets from smoking cigarettes.

And just as a craving for cigarettes is a sure sign of a confirmed smoker, a food craving may very well point to a food to which you are actually allergic. The leading proponent of this theory is Theron Randolph, M.D., a Chicago allergist, who told us that if you continue to eat foods to which you are allergically addicted, they will eventually make you chronically sick, even if they now give you temporary lifts.

To completely unravel a food allergy problem, you’ll have to sort out not only your symptoms but also exactly what’s in your diet. Food labels, unfortunately, do not spell out every last ingredients, natural and synthetic. ”Vegetable oil” can mean corn, soybean, peanut, sunflower, coconut, olive, cottonseed or other oils.

Sometimes labels are completely misleading. ”Nondairy” creamers and other dairy substitutes may contain whey, lactose or casein – all milk products. And manufacturers of so called standardized foods such as mayonnaise and ice cream are not obliged to list any ingredients at all. All that isn’t to discourage you, but to sharpen your awareness.

Dining out? Restaurant meals are a potpourri of several ingredients. Even a simple meatball sandwich may contain up to two dozen ingredients, including beef, soy, pork, onion, oil, butter, milk, egg, black pepper, wheat, rye, yeast, sugar, caramel and others.

Add a dash or two of catsup, and you add tomatoes, vinegar, corn, sweetener, onion powder, assorted spices and flavorings. No wonder food allergy can be a hard case to crack! To help you sort it all out, your doctor will probably ask you to be your own – or your child’s – detective. And the first step in solving this ”crime” against your health is gathering the clues.