What causes red-wine headaches? Is it sulfites?

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Dear Dr. Vinny,
What causes headaches among my friends who drink red wine? If it’s sulfites, aren’t they in organic wine?
—Bill H., Charlotte, N.C.
Dear Bill,
Red wine headaches don’t seem to have a single, identifiable cause, and have stumped many doctors, even fake ones like me.
You’re right that sulfites are often blamed, unfairly. All wines have sulfites—they occur naturally in the winemaking process. One of the tenets of organic winemaking is to not add any sulfites to the ones already there naturally as a byproduct of fermentation. Sulfites are effective at preventing spoilage, so I don’t blame winemakers for wanting to add more to wine. A small percentage of folks are sensitive to sulfites, and these allergies should be taken seriously. But a sulfite allergy does not typically manifest as a headache—it’s more like an asthma attack.
The histamines and tannins in red wines are another possible explanation. Some folks are histamine intolerant, but the link between histamines and headaches is unclear. Tannins—the puckery part of the skins and seeds of grapes, and also from oak barrels—can increase levels of serotonin, which can also be linked to headaches. Chocolate does the same serotonin thing, but you don’t hear much about chocolate headaches.
Whatever the cause, the alcohol in wine adds to the problem, as alcohol is known to trigger migraines in migraine-prone souls. And most wine lovers probably know that the dehydrating effect of alcohol can also make things worse.
You should tell your friends to talk to their doctors about their red wine headaches. In the meantime, it’s a good idea to proceed with caution. Start with half a glass of red wine and wait 20 minutes or so to see if it’s triggering a headache. If not, you can continue to enjoy your wine, but don’t overdo it, because then we’re talking about hangovers and not just red wine headaches.
—Dr. Vinny