Scientists may have figured out why so many people suffer from awful headaches after drinking wine, particularly red wine. Writing in Scientific Reports, researchers focused on phenolic flavonoids, which are chemical compounds found in grapes that affect the taste, color and mouthfeel of wine.

Various types of wine contain diverse levels of flavonoids. Red wine, in particular, can contain 10 times the amount of flavonoids than its white counterpart, thus making these compounds a major culprit for causing immediate wine headaches.When consumed, the alcohol in wine is metabolized in the liver by enzymes to create acetate. Primarily, the alcohol is turned into acetaldehyde. Then, acetaldehyde is converted to acetate.After conducting lab tests on more than a dozen compounds in red wine, researchers discovered that quercetin glucuronide (which is processed in the body from quercetin, a flavonol almost exclusively found in red wine) could block the enzyme that converts acetaldehyde into acetate.

When the enzyme is blocked, toxic acetaldehyde accumulates in the bloodstream, according to the researchers. High levels of acetaldehyde then result in headaches, nausea, facial flushing, and sweating. As for why some people are more prone to wine headaches than others, researchers admit that this information is still unclear. They are looking to conduct clinical trials soon in hopes of discovering that answer.

“We think we are finally on the right path toward explaining this millennia-old mystery,” Morris Levin, the director of the Headache Center at the University of California, San Francisco, informed The Guardian. “The next step is to test it scientifically on people who develop these headaches.”