Sulfites

Sulfites keep cut fruit from going brown, stop wine from turning, and hold dried apricots orange instead of the deep brown they become without them. They have been used for centuries, which is unusual for something that reads like a modern additive.

They also have a labelling rule of their own, and it sits in an awkward place relative to everything else people learn about reading labels.

The rule, and where it lives

Regulation names six of them: sulfur dioxide, sodium sulfite, sodium bisulfite, potassium bisulfite, sodium metabisulfite and potassium metabisulfite.

Ordinarily an ingredient present in an insignificant amount with no technical effect can be left off a label. For sulfites that exemption is narrowed almost to nothing: it applies only when no detectable amount is present, and the regulation then defines a detectable amount as 10 parts per million or more in the finished food, with the analytical methods specified.

So above 10 ppm, sulfites are declared. That is a real and unusually precise guarantee.

The gap that catches people

Sulfites are not one of the nine major food allergens. Milk, egg, fish, crustacean shellfish, tree nuts, wheat, peanuts, soybeans and sesame are the nine, and the statutory definition does not include sulfites.

That has one consequence and it is the reason this page exists. A “Contains” statement will never mention sulfites, because that statement exists to carry the nine. Someone who has learned the sensible habit of reading the allergen line first, and who reacts to sulfites, is reading the one line on the packet that cannot help them.

The information is on the label. It is in the ingredient list, under one of the six names above or as an E number in the 220s.

Who this actually matters to

A small proportion of people react to sulfites, and the reaction is most documented in people with asthma. This is not a food allergy in the immune sense that peanut allergy is, which is part of why sulfites sit outside the nine and inside their own rule.

For everyone else, sulfites are among the better understood preservatives in use, and they do a job that has an obvious alternative only if you are content with brown dried fruit and short-lived wine. The reason to learn the names is that you react to them, not that they are alarming in themselves, and the distinction between a hazard and an exposure that makes that sentence coherent is on the guide about it.

On skin

Sodium metabisulfite also appears in cosmetics, where it stops formulations oxidising, and it is a recognised contact allergen for a small number of people. If your skin reacts to products with no obvious common ingredient, it is one of the names worth checking against, which is the subject of the page for skin that reacts to everything.