"Contains sulfites" appears on wine labels in many countries, and a great many people have concluded from it that sulfites are the reason red wine gives them a headache.

The evidence for that is weak. The evidence for several other explanations is considerably stronger. It's worth going through, because a lot of people are avoiding the wrong thing.

What sulfites are and why they're there

Sulphur dioxide and related compounds have been used in winemaking for centuries. They act as an antioxidant, preventing browning and oxidative spoilage, and as an antimicrobial, suppressing unwanted yeasts and bacteria.

Fermentation also produces sulfites naturally, which means there is no such thing as a completely sulfite-free wine. Even wines with nothing added contain some, typically in the region of 10 milligrams per litre or so.

Legal limits vary by jurisdiction and by wine type, with sweet wines permitted higher levels because they need more protection. Typical dry red wine contains considerably less than the legal maximum.

The label is not a warning about headaches

Here's the source of the confusion. The labelling requirement exists because a small number of people have a genuine sulfite sensitivity, and it is primarily a respiratory issue.

The affected group is mainly people with asthma, and the reaction is bronchoconstriction — wheezing and breathing difficulty — not headache. Estimates of prevalence among asthmatics vary but it's a minority of that group, so a small fraction of the general population.

The label exists to protect those people. It was never a general health warning and it says nothing about headaches.

The dried apricot test

The most useful piece of evidence for anyone who suspects sulfites.

Dried fruit — particularly dried apricots, which are treated to retain their colour — contains sulfites at concentrations often many times higher than wine. So do some processed foods and certain fruit juices.

If sulfites were causing your headaches, a bag of dried apricots should reliably produce one. For the overwhelming majority of people who believe they're sulfite sensitive, it doesn't.

There's also the fact that white wine typically contains more added sulfite than red, because it lacks the protective tannins and pigments. Yet the headache complaint is overwhelmingly about red wine. That's close to the opposite of what a sulfite explanation would predict.

The likelier culprits

Alcohol. The obvious one, frequently dismissed because people think they haven't drunk enough. Alcohol is a diuretic and a vasodilator, both of which are associated with headache. Wine is also often consumed over a long evening with food, making it easy to underestimate the quantity. Modern red wines are frequently 14 percent or higher, meaning a large glass contains substantially more alcohol than people assume.

Dehydration. Compounding the above and largely preventable.

Histamines and tyramine. Biogenic amines present in fermented products, higher in red wine than white. There is some evidence linking these to headaches in susceptible individuals, and it fits the red-versus-white pattern better than sulfites do. The evidence is suggestive rather than conclusive.

Tannins. Have been proposed as triggering serotonin release in susceptible people. Again, fits the red wine pattern. Again, the evidence is not strong.

Congeners. Compounds other than ethanol produced during fermentation and ageing, present in higher quantities in darker drinks. Associated with worse hangovers in comparative studies of different spirits, and plausibly relevant here.

Quercetin. A flavanol present in red wine, proposed in relatively recent work as potentially interfering with alcohol metabolism and contributing to the specific red wine headache. Interesting hypothesis, not yet established.

The expectation factor

Worth mentioning honestly. Once somebody believes a substance causes them headaches, the belief itself contributes.

Nocebo effects are well documented and substantial in headache research specifically. Someone who reads a warning label, drinks the wine expecting a problem, and gets one, has had a real headache — the mechanism just may not be the one they think.

This isn't a dismissal. The headache is real. But it means self-reported sulfite sensitivity is unreliable evidence without blinded testing, which almost nobody does.

What to do if red wine hurts

Some practical experiments that are more likely to help than buying low-sulfite wine.

Try a lower-alcohol red — something at 12 or 12.5 percent rather than 14.5. If the problem improves, you have your answer and it wasn't sulfites.

Drink water alongside, properly, not one token glass at the end.

Try a white wine of similar alcohol on a separate occasion. If white is fine and red isn't at the same alcohol level, something in the red specifically is implicated — tannins, histamines, or something not yet identified — but not sulfites, since white generally has more.

Try a lighter-bodied, less tannic red. Gamay or a light Pinot Noir versus a heavy Shiraz.

And if you genuinely suspect a sulfite sensitivity, particularly if you're asthmatic and experiencing respiratory symptoms rather than headache, that's a conversation with a doctor rather than a wine writer.