A group of researchers from the University of California has finally solved a centuries-old mystery about why red wine can cause headaches. According to their study, which was published in the Journal of Agricultural and Food Chemistry, quercetin, a naturally occurring compound found in red wine, may be responsible for these headaches.

Quercetin is an antioxidant and a type of flavanol, which gives fruits and vegetables their color. When combined with red wine, it can disrupt a person’s ability to break down alcohol, leading to migraines, flushes, nausea, and headaches. Professor emeritus Andrew Waterhouse from the university’s viticulture and enology department explains that when quercetin gets into your bloodstream, your body converts it to quercetin glucuronide, which blocks the metabolism of alcohol. This can result in acetaldehyde accumulating in the body. Acetaldehyde is a toxin that can cause facial flushing, headache, and nausea.

Fellow researcher Dr Apramita Devi notes that high levels of acetaldehyde are more likely to trigger these symptoms in people who have pre-existing migraines or other headache conditions. Additionally, not all red wines have the same effect on causing headaches. The study suggests that factors such as sunlight exposure during grape growing season, aging time of the wine and the winemaking process influence whether a glass will trigger a headache. Wines from sunnier regions are more likely to have high quantities of quercetin and therefore more likely to cause near-immediate headaches.

Levin states that they are finally on track towards explaining this millennia-old mystery and the next step is to test this scientifically on people who develop these headaches with further experiments involving human subjects are needed to confirm this hypothesis fully.