rom the hand sanitizer at your favorite food truck to those single-use wipes at the doctor’s office, alcohols are used to disinfect things all the time.

So every time you have an alcoholic drink, it’s basically like microbe-killing juice… which doesn’t sound so great for the helpful critters in your gut. But, turns out, drinking in moderation could actually kill the microbes that cause food poisoning and diarrhea, while helping the bacteria that help you.

It’s been known for centuries that alcohols can kill microscopic germs—the Greek physician Galen used wine to clean gladiatorial wounds way back in 150 CE. But the ethanol in beer and wine is just one type of alcohol. Chemically, alcohols are compounds with at least one hydroxyl group, which is just a hydrogen and an oxygen, bound to a chain of at least one carbon .

High concentrations of alcohol—like the 70% isopropanol in antibacterial wipes—dissolve cell membranes, killing bacteria and viruses on contact. But a straight shot of vodka is only about 40% ethanol, while the average glass of wine is 12%, and beer is 5%. Even though they’re below membrane-nuking concentrations, lots of drinks can kill bacteria and viruses.

But exactly how is less clear. We know that lower concentrations of ethanol can still make cell membranes unstable. And they can promote the production of reactive oxygen metabolites, which can damage important cell parts.

So alcohol can knock out some unwelcome microbes in your stomach and upper intestine before they become harmful. For example, there’s pretty good evidence that beer and wine take out Vibrio cholerae—the bacterium that causes cholera, a disease where you’re attacked by uncontrollable diarrhea. That could be part of why alcohol was so popular on long sea voyages, and not just for Captain Jack Sparrow-types: it was safer to drink rum or beer than probably-contaminated water.

Booze doesn’t just kill cholera, either. Case studies have shown that wine, in particular, might be able to kill the nasty bugs that cause food poisoning like Salmonella and Norovirus, before they set up shop in your bowels. And one study on around 80 people found that drinking wine and other beverages with more than 10% alcohol kept people from being infected with hepatitis A from contaminated oysters, which can cause liver disease.

Of course, we now know that there are also beneficial bacteria that live on and inside us, and you wouldn’t want to kill a bunch of them with every shot of tequila. So it’s a good thing that doesn’t really happen, partially because a lot of the microbes that matter are in your colon, not your stomach. By the time your drink mixes with stomach acid and makes its way through your upper intestines, most of the alcohol is already absorbed.

That said, some scientists think a glass of wine every night could affect your lower intestines—in a good way. Some of the non-alcoholic compounds in wine called polyphenols feed helpful bacteria, and get broken into smaller useful molecules. Some scientists think these molecules can bind to the cell membranes of disease-causing bacteria, like those in the genus Clostridium, and kill them off.

Or they might even boost your health. One study suggested that polyphenol byproducts could explain why regular wine drinkers seem to have fewer heart problems. And another found that they might help counteract some of the metabolic problems caused by obesity.

But don’t go tapping that keg in celebration just yet. These potential benefits aren’t a sure thing, and they refer to moderate drinking—so, like, a glass of wine or a couple beers a day. Binge drinking and alcoholism are a totally different ballgame.

For example, a fairly large study published in 2001 found that regularly drinking a little alcohol seemed to reduce the chance of being infected with Helicobacter pylori, a bacterium that causes severe stomach ulcers. But the researchers found that drinking more wasn’t better. After a certain point, as alcohol consumption increased, so did the chance of infection.

In fact, the upper intestines in both short and long term heavy drinkers tend to have too much bacteria. Scientists think that large doses of alcohol could slow down intestinal movement and take a toll on helpful bacteria, which could give harmful microbes the time and space to gain a foothold. Alcohol can also mess with the genes in cells that line your intestines and stomach, which can lead to things like producing too much or almost no stomach acid after long term abuse.

And this isn’t great because stomach acid is one of the most effective defenses against disease-causing bacteria. Chronic alcohol abuse also cripples your immune system, making you much more vulnerable to pathogens in general. Not to mention the whole “destroying your liver” bit.

If you picture your gut lining as a sturdy trash bag made of cells, alcohols and their byproducts can punch a ton of little holes in it. This lets junk like bacterial toxins leak out, which your liver has to clean up. And the harder it has to work, the more damaged it becomes.

So a glass of red wine with dinner might actually help you resist some food poisoning. But if you go overboard, hangovers will be the least of your concerns. Thanks for watching this episode of SciShow, which was brought to you by our patrons on Patreon.

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