What Is Sulfite Sensitivity?

Overview

If you are facing discomfort or physical difficulties after a nice wine-tasting experience with your friends or a barbecue, this may be due to sulphite sensitivity.

Sulphite sensitivity, or sulphite allergy or intolerance, is characterised by adverse reactions to a group of chemical compounds called sulphites. These compounds will always include sulphur dioxide (SO₂), which is thought to be the root cause of sulphite sensitivity.¹ Sulphite sensitivity is not very common, with less than 2% of the population known to be affected. Keep reading further for more information on the causes, symptoms, diagnosis and management of sulphite sensitivity.

Understanding sulphites and where they are found

SO₂ is actually a gas! And one with impressive preservative properties.² You will find SO₂ in beverages and food to prevent spoiling. The modern age is not the first to notice the benefits of sulphites as preservatives. SO₂ is known to have been used as a fumigating agent by the ancient Greeks and as a sanitising agent by ancient Romans. It is a colourless and hideously pungent gas that dissolves in water like CO₂ in your favourite fizzy drink; only SO₂ dissolves to form sulfurous acid, a potent antioxidant and preservative. This prevents food from spoiling due to oxidation, and the acidity from sulphuric acid prevents the growth of harmful microbes. Today, sulphite additives are extensively used as antioxidants, preservative agents and anti-browning agents in a wide range of foods and drinks. Sulphites are also used in the pharmaceutical and cosmetics industries for their strong antioxidant properties and wide range of other industrial uses.²

On an ingredient label, SO₂ may be categorised as a food additive, with E-numbers ranging from E220 to E228. Other names of sulphites or sulphiting agents that may be helpful to look out for are potassium and sodium sulphites, bisulphites and metabisulphites.¹ Most foods that are shelf-stable have added sulphites. Dried or canned fruit and vegetables, fruit juices, processed meats, shelf-stable dressings, condiments and baked goods all tend to have sulphites to prevent spoiling. Certain beverages like wine and beer have naturally occurring sulphites in them from the fermentation process. Sulphite levels in white wines tend to be higher, as red wines have more natural tannins that fulfil the role of preservatives. Some fruits and vegetables like grapes, apricots and potatoes are typically sprayed with sulphites before transport to keep them fresh. Restaurants may also use sulphite powders or sprays on salads and crustaceans to preserve their colour.

What does sulphite sensitivity look like?

Reports of sulphite sensitivity only began to gather attention in the 1970s after widespread use. Primarily, an anaphylactic reaction was observed (swollen eyes, tongues, throat or lips, rapid heartbeat and laboured breathing) alongside a wide variety of other symptoms, including.³

• Urticaria (itchy red patches on the skin)
• Flushing (ruddy complexion, skin warm to touch)
• Diarrhoea and abdominal pain
• Dermatitis (swollen, blistered skin)
• Cyanosis (lack of oxygen in blood, bluish skin)
• Hypotension (low blood pressure, lightheadedness)
• Bronchoconstriction in asthmatic patients (trouble breathing)

Although sulphite sensitivity can be mild for some and usually are for most, for others, such as those with asthma, the reactions can be life-threatening. While the prevalence of sulphite sensitivity is less than 2% in the general population, the number rises to 13% amongst individuals with asthma, and sensitivity is likely to be more acute in these individuals.

Sulphite sensitivity can be triggered by ingesting food or beverages with sulphites, inhaling SO₂ from polluted air or pharmaceutical or cosmetic products such as aerosols (although they are not used as often nowadays), and 20 to 50 mg of sulphites is usually enough to trigger a reaction in sensitive individuals, with some being sensitive to even 5mg of ingested sulphites.³

Although you may see sulphur compounds in substances such as shampoos and soaps, it is important to note that sulphite sensitivity does not extend to these externally used products. Sodium laureth sulphate, for example, is a common surfactant that is used in most soaps, shampoos and household cleaners. These are molecularly different to SO2 and will not trigger sulphite sensitivity symptoms. Similarly, medicines (such as morphine sulphate) will have a sulphate component which will not react with the body the same way SO2 does and will therefore be safe to consume if you have sulphite sensitivity.

Why do I have sulphite sensitivity?

There are several explanations as to the why of sulphite sensitivity. Most prominently, it is thought to be linked with inefficient production of sulphite oxidase in the body - a mitochondrial enzyme, which is capable of oxidising sulphites to sulphates. This enzyme keeps the levels of sulphites generated naturally from amino acids cysteine and methionine steady and low. Usually, sulphite oxidase will convert the sulphites into a different form of sulphate that can be excreted in urine. When the enzyme production is low, or the enzymes are overwhelmed by the amount of sulphites in the body, the levels of sulphites may increase above normal levels. This may react with immune-system components, such as plasma cells, and trigger an immune response i.e. anaphylactic shock, dermatitis, etc.³ 

Moreover, sulphites, when ingested into the warm, acidic environment of our stomachs, are prone to be converted to SO₂ gas, which, when inhaled after burping, can cause bronchoconstriction (difficulty breathing), especially in those who have hyper-reactive airways. SO₂ will act as an allergen in the lungs, activating allergic antibodies - immunoglobin E, which can trigger an itchy throat and coughing fits.

The multiple possible mechanisms of sulphite sensitivity, coupled with variable symptoms and responses, make it difficult to diagnose and study. Even for the small percentage of affected individuals, simple skin tests which look at anti-sulphite plasma cells from immune responses are unreliable as levels of antigen may be transient; and the onus falls on the patient to work with an immunology or allergy specialist to keep a record of their diet and symptoms, which can help identify if they have sulphite sensitivity. Skin tests that look for dermatological reactions, blood tests to observe immune responses and antibodies, and an elimination diet alongside monitoring symptoms are a good start to accurately diagnosing sulphite sensitivity. 

Your doctor may also confirm sulphite sensitivity by a "challenge", where sulphite is administered in small doses of increasing concentration within twenty to thirty minutes of each other. The diagnosis is quicker this way, with the procedure taking only two to three hours. These doses are small enough to elicit only a mild asthmatic reaction, and the lung capacity is measured for each dose. The asthmatic reaction is quickly treated after measurement of lung capacity by broncho-dilating medication, which allows the air passages in the lungs to de-constrict and allow easy breathing. Your lung capacity will be studied further to determine whether you are sulphite-sensitive.

What can I do?

To reduce the chances of a reaction from sulphite sensitivity, take care in reading labels or cook meals at home to control and minimise sulphite exposure, prioritising fresh fruits, vegetables, and unprocessed foods that are less likely to contain sulphites. Ingredient labels are required to declare if they include sulphites, as they are recognised allergens.⁴ Meal planning is also a good way to ensure sulphite-free snacks and food are at hand when you need them. There are many communities which share and improve on sulphite-free recipes. When dining out, it is always a good idea to inform staff of allergies, even if you think the food is unlikely to have sulphites. This way, more people will be aware of what is happening in case you have an unlikely allergic reaction from cross-contamination or unknown sulphites in food and drink. Similarly, it is always good to inform friends and family of any allergies you may have so they know what is going on if anything happens.

If it is possible to get diagnosed, you may be prescribed medications, such as an epinephrine auto-injector, to manage anaphylactic reactions in case of accidental exposure. In any case, having an emergency response plan is key to feeling safe and secure in day-to-day life. Practicing epinephrine administration (if prescribed), familiarising oneself with seeking medical attention, and noticing when symptoms are worsening to request help on time is always a good idea.

Summary

Although rare, sulphite sensitivity is a condition that can have a significant impact on an individual's quality of life due to the pervasiveness of sulphites in our world today. Understanding the sources of sulphites, recognising the symptoms, and seeking appropriate diagnosis and management are essential steps for those affected by this condition. 

While sulphite sensitivity may present challenges in daily life, with proper education, dietary adjustments, and support, individuals can effectively manage their condition and enjoy a healthy and fulfilling lifestyle. Amongst high-risk groups, such as steroid-dependent asthmatics, caution is advised if symptoms are acute, and testing yourself for sulphite sensitivity might be a good idea. But in the general population, there is not much need to be wary of sulphite-containing substances unless you notice a marked pattern of sensitivity and disruption to daily life.