Sulphite Sensitivity; Not Officially an Allergy, Even Though It May Feel Like One

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Sulphites are everywhere; in our bodies and the air that we breathe, in our cosmetics and medications and in a lot of the foods that we eat and drink. Not only do they occur naturally in some foods, they are added to a great many more because of their considerable versatility, including their ability to act as preservatives, dough conditioning agents and bleaching agents. Unfortunately for some, sulphites can provoke a range of symptoms that look a lot like food allergy.

And now for the details, which include:

What is sulphite sensitivity?

Sulphites (or sulfites, depending on where you come from) are produced naturally in our bodies when we process sulphur-containing amino acids. They can also be found in fresh foods—like garlic, cabbage, onions, and eggs—and fermented foods and drinks—like sauerkraut, beer, and wine. However, it’s the sulphites that are added to food and drink by the food industry that are most likely to cause a problem for sulphite-sensitive people.

Sulphur dioxide was used throughout antiquity as a purifier; by the ancient Egyptians to clean their wine vessels, by the ancient Greek to fumigate their homes and by the ancient Romans to treat their wines. The first recorded use of sulphur as a food preservative dates back to in 1664, when someone suggested pouring cider into flasks while they still contained sulphur dioxide to prevent spoilage. By the 1800s, it was approved for use in the United States.

These days, sulphiting agents—sulphur dioxide and any compound that is capable of producing sulphur dioxide during the treatment of food, like sodium sulphate, and sodium/potassium bisulphite or metabisulphite—are widely used in the food industry as antioxidants and preservatives. They work by releasing sulphur dioxide which passes through the cell walls of microbes such as yeasts, bacteria and moulds, inhibiting their functioning and growth, thus helping to keep the food microbe-free and extending its shelf-life.

Sulphur dioxide also prevents non-enzymatic browning/oxidation in foods like dried fruits and dehydrated vegetables, and enzymatic browning in food like fresh fruits, shrimps and raw potatoes by preventing an enzyme called polyphenol oxidase (PPO) from working properly.

Sulphites can also function as dough conditioning agents and bleaching agents, they can prevent excess alkalinity of foods and they can be used as colour stabilisers. They are also used by the pharmaceutical industry to maintain the stability and potency of certain medications and cosmetics.

Unfortunately, sulphur dioxide can make some people ill. Although we don’t yet know exactly how, several possible mechanisms have been suggested:

1. Sulphur dioxide gas is released in the mouth and stomach when digestive acids react with sulphite-containing foods in these warm and accommodating environments. The gas then disperses into the airways, where it stimulates the parasympathetic system and provokes respiratory symptoms
2. Some people are deficient in the mitochondrial enzyme sulphite oxidase which is responsible for converting the sulphites (SO3) produced in the body during normal metabolism into inactive sulphates (SO4) that can be excreted in the urine. Without sufficient levels of this enzyme, the inhalation or ingestion of even more sulphites will lead to a toxic build-up in the body which will, in turn, trigger asthma-like symptoms
3. Sulphite sensitivity is a classic IgE-mediated immune response. This is implied by studies that have reported positive, immediate-type skin tests in people showing symptoms of asthma, hives (urticaria)/facial swelling (angio-oedema), and anaphylaxis, as well as positive basophil histamine-release tests with sulphites. In the 1990s, some researchers even reported finding a specific IgE antibody to sulphites, although their results have been generally overlooked by most researchers and allergists since then, for some unknown reason

The fact is, sulphite sensitivity in all its different forms is probably caused by all those mechanisms and possibly others that have not yet been discovered. However, since most studies have been unable to demonstrate an IgE-mediated mechanism, and the results of the 1990s study seems to have been lost in the sands of time, sulphites are thought to cause ‘true’ allergic reactions only very rarely and most allergists speak of sulphite ‘sensitivities’ and ‘intolerances’.

Sulphites are grouped with priority food allergens because people who are sensitive to these chemicals tend to react to them with allergy-like symptoms after eating, and are therefore sometimes assumed to have food allergies.

Because sulphites are cheap, convenient, and extremely versatile, their use by the food industry increased dramatically in the 1970s and 1980s, leading to a rash of reports of severe reactions to sulphites, including 7 deaths, often in restaurant customers frequenting salad bars.

This latter scenario is probably because the likelihood of a particular sulphited-food causing a reaction in someone depends on the ratio of free to bound sulphite. Lettuce happens to have few components with which sulphites can react, leaving most of the added sulphite free to provoke a reaction in sulphite-sensitive people. In contrast, sulphites added to potatoes and shrimp tend to be bound and are therefore not as likely to provoke reactions

The great salad bar intoxication led the American Food and Drug Administration (FDA) to ban the use of sulphites on raw fruits and vegetables in 1986. These days, several countries require food to be labelled as containing sulphites when the amount added exceeds 10 milligrams per kilogram or per litre—i.e. 10 parts per million (ppm) (See Reading Labels later)

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How common is sulphite sensitivity?

Over the past four decades, a number of efforts have been made to try and determine the prevalence of sulphite sensitivity. However, the studies have all differed in several ways; different dose and physical forms of the sulphiting agent used, different standards of evidence used to determine sulphite sensitivity and different opinions on the validity of the methods used to challenge patients in the first place. Most notably, the sample populations being given the sulphiting agent have been biased towards people with a history of sensitivity or those with severe asthma.

What this all boils down to is that we don’t really know the prevalence of sulphite sensitivity among the general population—people without asthma—although it’s thought to be very low. Some research puts it at around 1% and some at less than 0.05%.

And we’re not really sure about its prevalence among asthmatics, either, but it’s thought to be somewhere between 3% and 10%. It’s probably more towards the lower end of that scale because the general excitability of the lungs of asthmatics has probably contributed towards a bunch of false positive test results.

Of course, not everyone who is sensitive to sulphites has problems with sulphite-containing foods. Some people develop chronic skin symptoms because of a certain substance that they are coming into contact with regularly. A range of patch testing studies have been carried out among people with skin reactions and the results of those studies suggest that between 1% and 5% of the test subjects are reacting to sulphites that they are coming into contact with. Most of the reactions, when their source is identifiable, are due to topical medications, occupational exposure or cosmetics. (More about that later)

Sensitivity to sulphites can occur at any age; initial reactions often show up when people reach their 40s or 50s. That said, even though sulphite sensitivity is suspected more often in adults than in preschool children, young children can still have it.

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Risk factors for sulphite sensitivity

Researchers have identified several factors that can identify those who are at most risk of developing problems with sulphites.

The most obvious risk factor is the existence of severe asthma. Several studies have shown that asthmatics who have particularly hyperactive airways or require treatment with corticosteroids, like prednisone or methylprednisolone, are at an increased risk of having a reaction to food or drink that contains sulphites. One study carried out exclusively on children with steroid-dependent asthma found that 20% of them had sulphite sensitivity.

Symptoms are more likely to occur when the asthma is poorly controlled. When the asthma is under control, a person who has previously had reactions to sulphite-containing foods may be able to tolerate them again. Likewise, a sulphite-free diet has been shown to also improve the symptoms of chronic asthma in children, but such a diet has also proven difficult to follow.

Perhaps unsurprisingly, asthmatics tend to be more sensitive to sulphites that they inhale than sulphites that they eat.

Another risk factor for adverse reactions to sulphites is being female. Some studies have found that women are more at risk of asthma attack after eating sulphite-containing food and drinking sulphite-containing wine than men, and that girls are more sensitive to the sulphites contained in apple juice than boys.

A final risk factor for adverse reactions to sulphites is having a sensitivity to aspirin (salicylate). Several studies have shown that people with a sensitivity to aspirin are more likely to be intolerant to sulphites, too, and that symptoms of intolerance to both substances are very similar. Some people have even hypothesised that sulphites induce intolerance in the first place because of their aspirin-like properties.

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Symptoms of sulphite sensitivity

Symptoms of sulphite sensitivity resemble those of food allergy and can affect your skin, your breathing and/or your stomach and gut.

Reactions often occur within 2 to 30 minutes of ingesting the offending food or drink. The reaction tends to be at the more rapid end of the scale if the sulphites were ingested in a solution, like orange squash or a soft drink.

The severity of the reactions varies widely, ranging from mild—which is most often the case, even among the ‘at risk’ groups of asthmatics—to severe and even life-threatening.

Sometimes people experience difficulty in speaking (dysphonia), and a couple of cases of burning mouth syndrome—a random-seeming burning of the tongue, gums, lips, inside of the cheeks, or roof of the mouth that feels like you scalded yourself with a very hot drink—have also been reported.

However, by far the most common symptom reported by people suffering from sulphite sensitivity or allergy is asthma. The first reported case of asthma triggered by sulphur dioxide dates back to the eruption of Mt Vesuvius in 79 AD. While trying to make his escape and valiantly save some other people along the way, Pliny the Elder collapsed and died after spending a few hours inhaling the sulphurous gases emanating from the volcano. An explanation as to why he died and his fellow escapees did not was put forward by his nephew, Pliny the Younger: ‘The dense fumes choked his breathing and blocked his windpipe, which was constitutionally weak, narrow, and often inflamed’.

Back in modern times, one of the first reports to suggest that the ingestion of food containing sulphites could cause irritation of the respiratory tract was published in 1973. Since that study was published, many more have reported symptoms of breathing problems, including:

• Cases of asthma—with symptoms including coughing, wheezing, shortness of breath and chest tightness
• Bronchospasm—a sudden constriction of the muscles in the walls of the bronchioles, leading to feelings of chest pain/tightness. In restaurants, this sudden choking sensation has been incorrectly attributed to the aspiration of food
• Bronchoconstriction—a narrowing of the airways which makes it more difficult to breathe and leads to coughing, wheezing, and shortness of breath

Skin, gastrointestinal, and respiratory reactions can occur simultaneously, or in various combinations and level of severity.

Very rarely, sulphites have been shown to cause anaphylaxis after eating sulphite-containing foods, drinking wine or drinking sparkling water.

Because of its omnipresence, as well as triggering episodic and acute symptoms, sulphites can cause chronic skin and respiratory symptoms.

Sulphite-sensitive people who regularly use medical creams or cosmetics that contain sulphites are likely to exhibit chronic skin symptoms, especially on the hands and face. Occupational exposure to sulphites will also cause persistent skin symptoms.

Occupational exposure to sulphites can also contribute to chronic symptoms of asthma, as can regular exposure to sulphite additives in foods and certain medications, including asthma medications! (see Non-food sources of sulphites later)

Pro tip: If you have a constant, annoying rash or find that you’re often wheezing, reducing your exposure to sulphites may alleviate your symptoms

Threshold for reactions

People who are sensitive or allergic to sulphite vary in their degree of intolerance, each person needing to reach a specific threshold of exposure before a reaction occurs; a food that will trigger a reaction in one person may be tolerated by another.

According to a review panel of the European Food Safety Authority (EFSA), the smallest quantity known to have triggered a reaction was between 1 and 5 mg of potassium metabisulphite (equivalent to 3.7 mg of free SO2).

However, current labelling laws only require food containing more than 10 mg of sulphite per kilo to be labelled because current technology cannot detect smaller amounts in food.

What this means in terms of real food is that someone with an actual threshold of 10 mg would need to eat about 200 g of food containing 50 ppm (low to moderate levels) of sulphite—for example: avocado dip, frozen potatoes, fresh mushrooms or fresh shrimp—to provoke a reaction. But much less food containing moderate levels of sulphite—for example, between 20g and 100 g of grape juice or sauerkraut (at 100 to 5000 ppm)—and very small amounts of foods very high in sulphite, such as dried fruits which, at levels of 2000 ppm (less than the legal amount of 3000 ppm in countries like Australia) would only require about 5 g to prompt a reaction.

Your threshold can be lowered and your allergic reactions worsened by things called ‘cofactors’. Cofactors include things like how much you eat and whether those ingredients have been cooked or processed, as well as exercise, infection, anti-inflammatory drugs, alcohol, and stress.

Exercise may hit people who are allergic to sulphite with a double-whammy. Studies that have looked into the effect of pollution on exercising asthmatics have shown that they can suffer from breathing problems when they breathe in as little as 0.10 parts per million of sulphur dioxide for 10 min, and that the effect is worsened because they—as do we all—have a greater tendency to breathe through their mouths when they exercise, and the nose removes sulphur dioxide from the air we breathe in more effectively than the mouth.

Cofactors’ are thought to play a role in about 14% to 30% of all anaphylactic reactions.

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Diagnosing sulphite sensitivity

Diagnosing sulphite sensitivity is a tricky business.

A diagnosis will primarily be based on your clinical history—a record of consistent symptoms following the consumption of sulphite-containing foods. This will require you to provide your allergist with answers to questions about your general medical background (including any other allergies you may have and relevant illnesses in your family) and your dietary history (what you ate to provoke your symptoms, what those symptoms were, how long they lasted, whether you had exercised or taken painkillers and many other details).

Unfortunately, the large variety of signs and symptoms associated with sulphite sensitivity makes diagnosis on the basis of history alone very difficult. However, it is the most practical method as there are currently no uniformly accepted standard protocols for challenging people with sulphite sensitivity; the dose and physical form of sulphite varies widely from test to test, as do the individual responses to each method, which is also one of the main reasons that there continues to be controversy over the actual prevalence of sulphite sensitivity.

The usual skin and blood tests often produce no response, although you may be asked to take a skin prick test if the doctor suspects a sulphite allergy based on your clinical history. If that produces a negative results, the doctor may do an intradermal test, during which an extremely dilute sulphite solution (as a general rule, doses for intradermal tests are 100- to 1,000- fold more dilute than the concentration used for prick tests) will be injected under your skin. This kind of testing tends to be more sensitive but will also often produce a negative result as sulphite sensitivity often does not seem to be IgE-mediated.

The only way in which your doctor can reliably diagnose sulphite sensitivity is to carry out an oral challenge test, during which you will be asked to ingest a sulphite compound—sodium metabisulphite, sodium bisulphite or potassium metabisulphite—either in capsules or solutions of increasing concentration while your lung function and vital signs are monitored.

This type of challenge can result in severe reactions so, if it is attempted, it is normally undertaken in a hospital environment and very small doses of sulphite are used (from 1 to 200 mg). In most cases, the initial dose will be too mild to provoke any reactions at all. The doctor will wait about half an hour before giving you the next, higher dose. You may be asked to hold the solution in your mouth for a short while before swallowing, to allow time for the sulphur dioxide gas to form.

As soon as a reaction takes place, your lung function will be measured—usually by spirometry. People who are sensitive to sulphites tend to react to them with a decrease in FEV1—Forced Expiratory Volume in one second, that is, the volume of air that someone can exhale in the first second of a forced breath after maximal inspiration—of more than 20%. The entire procedure should take about 2 to 2.5 hours.

Sometimes, a doctor may recommend an elimination diet during which you will be asked to avoid foods that contain sulphites. If this makes your symptoms go away and improves your general health, it’s a good indication that you may be sensitive to sulphites. The diet may then be followed by an oral challenge to a sulphite-containing food, just to make sure.

A 1996 study showed that following an elimination diet for a month seemed to make asthmatics who were suspected of sensitivity to food additives even more sensitive to sulphites, thus making the results of a subsequent oral challenge more reliable.

For those who suffer from contact reactions to sulphites, there is better news: contact dermatitis due to sulphite sensitivity is much easier to diagnose, using patch testing.

This kind of test generally involves three visits to an allergist within a one-week period.

• During the first visit, substances—often sodium metabisulphite—are applied to your back (or occasionally your arms or thighs) using small metallic discs held in place by hypoallergenic tape. Any reactions—like redness, inflammation or swelling—are noted after 20 minutes
• Then you leave, with the discs still taped in place, and return for your next examination 48 hours later, when any reactions are noted. The patches are then removed
• Finally, you return for your last exam after a total of 72 or 96 hours have passed since the substances were placed against your skin

Patch testing has been shown to be quite reliable.

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Good to know

Vitamin B12 may prevent reactions in some people with sulphite sensitivity.

Some people with sulphite sensitivity are thought to lack sulphite oxidase enzymes, which means that they are unable to break down the excess sulphites that they breath in or ingest, resulting in a build-up of sulphites in their bodies which prompts allergy-like symptoms. Vitamin B12, however, is able to catalyse this extra sulphite without the presence of enzymes and should therefore, in theory, be able to prevent the toxic build-up of sulphites in the body and the associated symptoms.

This was first put forward as a possibility in 1986 by two scientists (Simon and Wasserman) who reported that giving 6 sulphite-sensitive patients 1– 5 mg of vitamin B12 (cyanocobalamin) either partially (in 2) or completely (in 4) blocked their symptoms of bronchoconstriction.

In a 1992 study designed to examine the mechanisms of sulphite sensitivity, 5 boys with asthma and metabisulphite intolerance were challenged with potassium metabisulphite, first by itself and then after taking some cyanocobalamin (a man-made vitamin B12 compound). After taking the vitamin compound, 4 of the 5 children were able to pass the challenge, reaching the maximum dose of potassium metabisulphite (which was at least twice what they could normally handle) without showing any symptoms.

3 of the 4 boys who passed the challenge were re-challenged 4 to 13 days later, and were still able to tolerate the maximum dose of potassium metabisulphite. The challenge was repeated again, this time between 12 to 270 days later, and the boys failed the challenge; 2 of the boys’ thresholds had gone back down to their original amount, but the other 2 could handle more than they could originally. However, for a few days, the vitamin B compound that they had taken had suppressed their reactions.

Some experts have suggested that the increased demands on vitamin B12 to metabolise the sulphites present in the food and drinks that we ingest may explain why so many people seem to suffer from a vitamin B12 deficiency nowadays, apart from low dietary intake.

Note that the recommended daily amount of vitamin B-12 for adults is 2.4 micrograms (mcg) and for young children, half that. Although high doses of vitamin B12 seem to be safe, it can cause side-effects like headaches and diarrhoea and also interfere with the working of some medications, so if you’re considering taking vitamin B12 to prevent the symptoms of sulphite sensitivity, you might want to consult your doctor first.

Working with sulphitecan be decidedly hazardous for your health.

Exposure to sulphites has been has been reported to cause a variety of allergic reactions in a variety of professions, including;

• acute contact dermatitis in a baker
• hand dermatitis, swelling, rashes and itching eyelids in a hairdresser
• asthma in a potato processing-plant worker
• asthma in a radiographer
• contact dermatitis and asthma in a photographic technician
• dermatosis in pharmaceutical factory workers
• asthma in sulphite mill workers
• asthma and vocal cord dysfunction in a trawlerman and two prawn processors
• and death by suffocation in a couple of shrimp trawlermen

Sulphites are bad for your (gut) health and, as a result, your allergic status.

Whether you’re allergic to them or not, a 2017 study has shown that high levels of sulphites are no good for your gut’s microbiome. This can come as no surprise considering we use them to kill off the bacteria in our food and drink. Concentrations of sodium sulphites between 250–1000 parts per million (ppm) can inhibit the growth of and even start killing off (at least) 4 of the beneficial bacteria—Lactobacillus casei, plantarum and rhamnosus, and Streptococcus thermophilus—that can live in the gut. These may sound like relatively high concentrations of sulphites, but even ‘healthy’ dried fruit can contain up to 2000 ppm in Europe (and 3000 ppm in Australia).

According to the World Health Organisation, most of us regularly exceed the daily amounts of sulphites that are considered ’safe’ in our diets. In 2022, the European Food Safety Authority (EFSA) also raised concerns that consumers who ate a lot of sulphited food products (those in every age group except adolescents) may be taking in too many sulphites on a daily basis but, due to a lack of available scientific data, they were unable to calculate Acceptable Daily Intake (ADI)—the threshold below which the daily intake is safe.

And the sulphites we are exposed to in our drugs and cosmetics and in the air we breathe count towards our ‘daily allowance’, too.

Considering the raft of recent research showing that dysbiosis—an imbalance in the microbial communities in the gut and elsewhere—can lead to food allergy and intolerances, as well as several other health problems, chances are, even if you didn’t have a food-related health issue before you started eating a highly sulphited diet, you’ll end up developing one.

Sulphited food for thought.

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