What Exactly Are Sulfites? A Comprehensive Guide

December 28, 2025 •

4 min read

According to the Australasian Society of Clinical Immunology and Allergy, roughly 5-10% of people with asthma may experience adverse reactions to sulfites. These compounds are naturally occurring substances and common food additives with a long history of use, but they remain a source of confusion and concern for many consumers.

Quick Summary

Sulfites are sulfur-based chemical compounds used as preservatives and antioxidants to prevent microbial spoilage and browning. They are found naturally in some foods and are also added to many processed products and wine, requiring labeling above certain concentrations due to potential sensitivities, particularly among individuals with asthma.

Key Points

Sulfite Definition: Sulfites are chemical compounds containing the sulfite ion ($SO_3^{2-}$), often functioning as preservatives and antioxidants in food and beverages to prevent spoilage and browning.
Natural and Added Sources: These compounds occur naturally during fermentation (e.g., in wine) and are also added to processed foods like dried fruits, bottled juices, and certain seafood.
Allergy vs. Sensitivity: A true sulfite allergy is rare; more common is a sensitivity, which can trigger asthma attacks or allergic-like symptoms in susceptible individuals, particularly those with pre-existing asthma.
Reading Labels is Key: Due to potential health effects, regulations require food and beverage labels to declare sulfites when present above 10 ppm, often using code numbers E220-E228 or listing specific sulfite names.
Misconception about Wine Headaches: Sulfites are an unlikely cause of headaches from wine for most people; other factors like tannins or histamines are more probable culprits.
Sulfite vs. Sulfate: Sulfites are chemically distinct from sulfates, which are used in many medications and detergents and generally do not cause reactions in sulfite-sensitive individuals.

The Chemical Nature of Sulfites

At their core, sulfites are inorganic salts containing the sulfite ion ($SO_3^{2-}$). They are closely related to sulfur dioxide ($SO_2$), a gas that is the active component released by sulfites when used as a preservative. In food science, the term 'sulfites' often refers to a group of substances including sulfur dioxide, sodium sulfite, and potassium metabisulfite.

How Do Sulfites Function as Preservatives?

Sulfites primarily act in two ways to preserve food and beverages:

As Antioxidants: They prevent oxidation, the chemical reaction responsible for browning in dried fruits or the spoilage of wine. By binding to oxygen, they stabilize the color and flavor of the product.
As Antimicrobials: They inhibit the growth of bacteria, fungi, and yeasts, extending the product's shelf life. This is crucial in products like wine, where they protect against unwanted microbial activity.

Common Sources of Sulfites

Sulfites can be found in a wide array of foods and drinks, both naturally occurring and added. The FDA requires manufacturers to declare sulfites on labels if their concentration exceeds 10 parts per million (ppm).

Foods and Beverages that Contain Sulfites

Wine: Sulfites are a natural byproduct of fermentation but are also often added during winemaking to prevent oxidation and spoilage. White wines and sweeter wines generally have higher sulfite concentrations than red wines.
Dried Fruits: Ingredients like dried apricots are often treated with sulfites to preserve their bright color and prevent browning. The sulfite content in dried fruits is significantly higher than in wine.
Processed Meats: Cured meats, sausages, and hot dogs may contain sulfites as a preservative.
Bottled Juices: Commercial lemon and lime juices and some grape juices often have sulfites added to extend their shelf life.
Condiments and Sauces: Pickles, salad dressings, and molasses can contain sulfites.
Seafood: Fresh and frozen shrimp are sometimes treated with sulfites to prevent discoloration.
Medications: Some eye drops, injectable medications, and oral medications may contain sulfites as a preservative.

Sulfites, Allergies, and Sensitivities

While most people can consume sulfites without issue, some individuals experience adverse reactions. It is important to distinguish between a true IgE-mediated allergy and a sensitivity, which is more common and does not involve the immune system.

Reactions to Sulfites

The most common adverse reactions to sulfites are seen in individuals with asthma. When asthmatics inhale the sulfur dioxide gas released by sulfites, it can cause airway irritation and narrowing, leading to respiratory symptoms. Symptoms of sulfite sensitivity may include:

Respiratory: Wheezing, shortness of breath, chest tightness, and coughing.
Dermatological: Hives (urticaria), flushing, and skin rashes.
Gastrointestinal: Stomach pain, abdominal cramps, and diarrhea.
Anaphylaxis: While extremely rare, severe allergic reactions like anaphylaxis have been reported in some very sensitive individuals.

The Sulfite vs. Sulfate vs. Sulfur Distinction

Consumer confusion often arises from the similarity in terms for sulfur-based compounds. Sulfites should not be conflated with sulfates or elemental sulfur, as they have different chemical compositions and functions.

Comparison of Sulfur Compounds


Feature	Sulfite ($SO_3^{2-}$)	Sulfate ($SO_4^{2-}$)	Sulfur (S)
Chemical Formula	$SO_3^{2-}$ (one sulfur, three oxygen atoms)	$SO_4^{2-}$ (one sulfur, four oxygen atoms)	S (elemental sulfur)
Primary Use	Food preservative, antioxidant, antimicrobial	Used in fertilizers, detergents, and some medications like morphine sulfate	Applied as a fungicide in vineyards and used in industrial processes
Reaction Type	Can trigger sensitivity in asthmatics; some can be oxidized to sulfates	Generally does not cause reactions in sulfite-sensitive people	Inhaled elemental sulfur can cause breathing difficulty
Oxidation State	Sulfur is in the +4 oxidation state	Sulfur is in its maximum oxidation state of +6	Sulfur is in the 0 oxidation state

Are Wine Headaches Caused by Sulfites?

Many people attribute headaches after drinking wine to sulfites, but this is a common misconception. Research suggests that unless you have a sulfite sensitivity, sulfites are an unlikely cause. The levels in wine are relatively low compared to dried fruit. Other culprits, such as histamines, tannins, or simple dehydration, are often the real cause.

Labeling Regulations and Safe Consumption

Due to potential health risks for sensitive individuals, food labeling is an important regulatory tool. While labeling requirements vary by country, the general rule is to declare sulfites if they are present above 10 ppm.

How to Identify Sulfites on a Label

Look for the word 'sulfites' or the full name of the chemical, such as 'sodium sulfite' or 'potassium metabisulfite'. In Europe, sulfites are part of the top 14 allergens and are bolded on labels. The additive code numbers E220 to E228 also indicate the presence of sulfites. Reading labels carefully is crucial for anyone with a known sensitivity.

Navigating a Sulfite-Reduced Diet

For individuals with a diagnosed sulfite sensitivity, minimizing intake requires careful food selection. Prioritizing fresh, unprocessed foods is key. Organic wines, though not completely sulfite-free due to natural fermentation, are often made with no added sulfites. Cooking at home from raw ingredients also provides better control over additives.

Conclusion

Understanding what exactly are sulfites involves recognizing them as a group of useful chemical compounds that act as preservatives and antioxidants in a wide range of products. While generally safe for most, they can trigger adverse reactions in a sensitive portion of the population, especially those with asthma. By being aware of their function, common sources, and the difference from other sulfur compounds, consumers can make informed decisions and better manage their dietary intake. Label reading is the most effective tool for avoiding sulfites, and for most, concerns about mild headaches from sources like wine are often misguided.

Frequently Asked Questions

Sulfites are added to food and drinks primarily to act as preservatives and antioxidants. This helps to prevent microbial growth from bacteria and fungi, and it inhibits oxidation, which can cause discoloration and spoilage.

No, sulfites and sulfates are different chemical compounds. Sulfites contain a sulfur atom bonded to three oxygen atoms ($SO_3^{2-}$), while sulfates have a sulfur atom bonded to four oxygen atoms ($SO_4^{2-}$). Sulfates are found in many different products and generally do not trigger reactions in sulfite-sensitive individuals.

Common sources of sulfites include wine, beer, dried fruits (like apricots), bottled lemon and lime juice, processed meats (sausages), certain sauces, and some canned and frozen seafood.

While severe, true allergies are rare, sulfites can cause allergic-like symptoms and asthma attacks, particularly in those with pre-existing asthma. Reactions like wheezing, hives, and stomach pain are most often due to a sensitivity rather than a true immune-system allergy.

Yes, all wines contain at least some sulfites, as they are a natural byproduct of the fermentation process. However, some winemakers add additional sulfites, and this must be disclosed on the label if the concentration exceeds 10 ppm.

Researchers believe that in sensitive individuals, inhaling the sulfur dioxide gas released by sulfites can irritate the airways and cause constriction. It may also involve a lack of the enzyme sulfite oxidase, which breaks down sulfites in the body.

For those with sensitivity, the best way to avoid sulfites is to read food and medication labels carefully. Focus on eating fresh, whole foods and be aware of common high-sulfite items like dried fruits and some bottled juices.