From the Allergic Living archives. First published in the magazine in 2005.
Consider the Canadian Food Inspection Agency’s list of the top 10 food groups that cause the most frequent and severe allergic reactions. Nine of the names will be familiar to most Canadians — peanuts, tree nuts, milk, eggs, fish and shellfish, soy, wheat and sesame seeds.
But the tenth name on the list may surprise: sulphites. These are the chemical additives used to stop food from browning or spoiling. In 1 per cent of the population, mostly those with asthma, even tiny amounts of sulphites can cause reactions. An estimated 4 per cent of asthmatics are sensitive to them.
In Canada, there have been reports of more than 100 sulphite-related reactions, ranging from nausea and abdominal pain to anaphylactic attacks. At least one Canadian has died.
Although sulphites are known to trigger symptoms in susceptible individuals that appear to be allergic reactions, including anaphylaxis, scientists still don’t know how they do this. Unlike the other food groups on the list, sulphites are chemicals, not proteins.
Researchers don’t yet know whether sulphites cause the immune systems of some people to respond abnormally or whether they set off some other mechanism that causes allergic-like reactions. The researchers also haven’t figured out why sulphites pose a threat to some people and not to others.
One theory is that people sensitive to sulphites have a genetic abnormality that hinders the body’s breakdown of these chemicals. However, Dr. Susan Tarlo, a respiratory physician at Toronto’s University Health Network and a specialist in lung disease and allergic response, says her extensive research does not confirm that theory. Another theory links sulphite sensitivity to a lack of B12 vitamins, but that research is still not conclusive.
If you develop hives or have trouble breathing after a restaurant dinner and a glass of wine and suspect you may have this sensitivity, the first step is to see an allergist and confirm what is causing your reaction.
The only way to be sure that it is a sulphite sensitivity is to undergo an oral challenge in a hospital setting. In such a test, doctors will give you a glass of juice with sulphites to see whether you respond. (For sulphites, Tarlo says a skin test is not reliable enough.)
The food inspection agency has added sulphites to its top 10 allergens list because they cause allergic-like reactions in such a significant number of people. (One per cent of the Canadian population equates to about 320,000 individuals.) But there is no scientific evidence that the prevalence of sulphite sensitivity has actually increased over the past years.