Why do some people get headaches from drinking red wine?

A study published in the journal Scientific Reports explored the reason why red wine causes headaches in some subjects who can drink other alcoholic beverages without suffering. The cause for this effect has been attributed to a number of components, often the high level of phenolics in red wine, but a mechanism has been elusive.
In the study researchers discovered that red wine’s rich flavonol content, specifically quercetin, impacts how the body metabolizes alcohol, which can result in a headache. Quercetin is naturally present in all kinds of fruits and vegetables, including grapes. It’s considered a healthy antioxidant. Corresponding author of the study Andrew Waterhouse, professor emeritus with the UC Davis Department of Viticulture and Enology explained “When it gets in your bloodstream, your body converts it to a different form called quercetin glucuronide. In that form, it blocks the metabolism of alcohol.” Waterhouse said levels of this flavanol can vary dramatically in red wine
As a result of quercetin blocking alcohol metabolism, people can end up accumulating acetaldehyde which is a well-known toxin, irritant and inflammatory substance that can cause facial flushing, headache and nausea.
Scientists will next compare red wines that contain a lot of quercetin with those that have very little to test their theory about red wine headaches on people.
Researchers said there are still many unknowns about the causes of red wine headaches. It’s unclear why some people seem more susceptible to them than others. Researchers don’t know if the enzymes of people who suffer from red wine headaches are more easily inhibited by quercetin or if they are just more easily affected by the buildup of the toxin acetaldehyde.
Source: Devi, A., Levin, M. & Waterhouse, A.L. Inhibition of ALDH2 by quercetin glucuronide suggests a new hypothesis to explain red wine headaches. Sci Rep 13, 19503 (2023).