A glass of red wine might complement a turkey dinner nicely, but even a slight amount can trigger headaches for certain individuals. The notorious “red wine headache” can kick in anywhere from 30 minutes to three hours following the consumption of just a small glass. According to a research published November 20 in the journal Scientific Reports, scientists from the University of California, Davis and the University of California, San Francisco believe they have identified the trigger.

[Related: Red wine’s composition is a mix of chemicals that can make some individuals feel awful.]

The group theorizes that a natural flavanol present in red wines can disrupt our body’s normal processing of alcohol, potentially leading to a headache. This flavanol, known as quercetin, can be found in several kinds of fruits and vegetables, including grapes. Although quercetin is regarded as a beneficial antioxidant and can even be ingested as a supplement, it might pose a problem when metabolized with alcohol.

“Once it enters your bloodstream, your body alters it into a different form referred to as quercetin glucuronide,” explains study co-author and UC Davis wine chemist Andrew Waterhouse in a statement. “This form inhibits the metabolism of alcohol.”

The end product is a build-up of a harmful substance known as acetaldehyde.

“Acetaldehyde is widely recognised as a damaging, irritant and inflammatory substance,” expressed Apramita Devi, a UC Davis microbiologist and co-author of the study. “It is scientifically accepted that elevated levels of acetaldehyde can result in symptoms such as facial redness, headaches and feelings of nausea.”

A drug namely, disulfiram, which is frequently prescribed to patients battling alcohol dependence as a deterrent for drinking, is known to trigger similar effects when alcohol is consumed. Disulfiram also leads to the accumulation of acetaldehyde resulting from alcohol consumption by interfering with a certain enzyme in the human body typically involved in its breakdown. It is estimated that close to 40% of the East Asian population possess enzymes capable of metabolizing alcohol that cause a build-up of acetaldehyde in their system.

“Our hypothesis is that susceptible individuals who consume even moderate amounts of wine containing quercetin can experience headaches, especially if they have a pre-existing condition such as migraines or other primary headache disorders,” expressed Morris Levin, a neurologist at the University of California, San Francisco and co-author of the study. “We believe we are finally close to understanding this ancient conundrum. The succeeding step is to scientifically test this on individuals who experience these headaches. So, keep a lookout for updates.”

According to the team, sunlight increases the headache-causing flavanol in the grapes grown to make wine.

[Related: Can I be allergic to alcohol?]

“If you grow grapes with the clusters exposed, such as they do in the Napa Valley for their cabernets, you get much higher levels of quercetin. In some cases, it can be four to five times higher,” said Waterhouse.

Levels of quercetin can differ depending on how the wine is made, including skin contact during fermentation, the fining processes, and even aging.

The research advises that numerous uncertainties still exist regarding the origins of red wine migraines. Despite having a deeper comprehension of the biological mechanisms related to red wine headaches, it’s still unclear why some individuals are more susceptible than others. The team is conducting comparisons of red wines with high quercetin content such as shiraz, versus those with less, to examine their theory that quercetin is genuinely the trigger for red wine headaches. They’re also intrigued as to whether the enzymes of frequent red wine headache sufferers are more easily obstructed by flavanol, or if this demographic is more affected by the accumulation of the acetaldehyde poison.

“If our hypothesis proves correct, we’ll then have the means to begin addressing these significant queries,” said Waterhouse.