Locating allergies can be one of the most difficult of detective jobs. Most elimination diets are too simplistic, which is why they don't seem to help people. The biggest problem is that allergies are far more complicated than most people appreciate.

First suspect foods that are normally eaten more than twice a week (wheat, potato, cow's milk products, tomato, eggs, yeast, sugar, tea, coffee, cocoa, maize (American corn), rice and one or more spices, although other foods may be suspect, too).

Exclude the suspect food components from your diet for at least six days. In most cases, you will improve, should the excluded food or foods be to blame for your problems.

If you suspect quite a number of foods, you may spread the testing over two or three periods of six days, spaced a week apart, eliminating different foods during different six-day periods. This will also avoid creating even a temporary nutritional imbalance.

Various allergic reactions tend to disappear during different test periods, so that, for example, frequent headaches and dry skin patches may disappear during the first six days; insomnia during the second, and loose bowel (or constipation) and congested sinuses during the third.

An unusually strong craving may point to a food to which you are sensitive. You can confirm your suspicion by re-introducing a single food you think most likely to be the major "offending" item, for up to the first three days of a seven-day period at the beginning of which you are free of your symptoms. Make sure to keep other variables stable during these challenge tests. You should also keep a food diary when doing these challenges, recording next to the food the time you've eaten it, and then the time, duration and type of reaction, with a grading for severity.

Seven common pitfalls and conundrums:

All foods are members of many diverse food families. Two well known food "families" include those containing gluten wheat, rye, barley (or malt), and oats and the nightshade family: potato, tomato, tobacco, aubergine (eggplant), peri-peri, chili, bell peppers and paprika. If you are sensitive to one food, it's likely that you're also be sensitive to others in the particular food family.

Many foods are composites. For example, sandwich loaf bread usually contains milk, sugar and yeast, in addition to wheat; ketchup contains sugar and citric acid, in addition to tomato. It's essential to find out the complete ingredients of what you eat so as to eliminate offenders completely.

People often feel worse initially. They can experience headaches, wooziness, or flu-like symptoms, particularly on days two and three of the elimination. It means there probably is a sensitivity to the eliminated foods.

There could be delayed reactions that overlap the six-day periods. If you suspect this, increase the spacing between the food challenges.

Your body does not regard all allergens as equally threatening. Minor threats are often ignored, as long as major threats are about. This can account for the disappearance of previously experienced allergies. These will reappear a little while after the elimination of the major allergen, which was distracting your immune system.

Remember that domestic gas, nutritional supplements, medicines, aromatic and other oils, paraffin (kerosene in America), cosmetics, paints and varnishes and even toothpaste can also be a source of your problems.

Your body can take from one week to as long as six weeks before improving after some foods have been eliminated, but this is rare.

I tend to prefer this procedure over blood tests, which may indicate an allergy but not which food is linked to symptoms. Testing can also not tell you about food "intolerances", where your body, say, lacks some enzyme and cannot properly cope with the corresponding food.

Prick or scratch tests are less reliable for identifying food sensitivities, but very useful for environmental allergens like fungus spores, pollen, house dust mites, animal hair and the like.

Harald Gaier is a registered naturopath, homeopath and osteopath.

(c) 1995 Harald Gaier