What Happens if You Drink Spoiled Milk?

If you learn one thing about milk, let it be this: Unlike cheese, it doesn’t get better with age. A tall pour of spoiled milk from a weeks-old gallon in the back of your fridge is not a great idea. But how does milk go bad and what actually happens to your gut if you drink spoiled milk? Keep reading to find out.

“Milk curdles in part because of bacteria,” says Niket Sonpal, MD, a gastroenterologist and internist at Touro College of Osteopathic Medicine in New York City. “Even if milk is pasteurized, there’s still a certain amount of milk bacteria left behind that will eventually cause the milk to spoil and curdle.”

Dr. Sonpal notes that both salmonella and E. coli have been found in pasteurized milks. And as a hard-and-fast rule, he recommends avoiding milk that hasn’t been pasteurized (“raw” milk). According to Jennifer Maeng, RD, a dietitian in New York City, raw milk “contains a lot of pathogenic bacteria and poses a high risk to those who consume it.”

Although refrigeration slows the process, it doesn’t fully prevent milk from spoiling. Opened milk that’s kept in a refrigerator typically goes bad within 4 to 7 days of the printed best-by date, says Maeng. “If milk is unopened and left in the refrigerator, it can usually last an extra 5 to 10 days past the printed date, depending on the fat percentage of the milk,” she adds.

No matter the label, if your milk smells “off,” that’s a pretty clear indicator that it has gone bad. But a funky smell is not the only indicator. According to Maeng, a sour taste, change in color, or change in appearance are also telltale signs that your milk has gone bad.

Sour and spoiled are not synonymous when it comes to milk. “Sour milk is a dairy product that is safe to consume, while spoiled milk is not safe to consume,” Maeng says. “Sour milk is produced by either a fermentation process or by adding an acid, such as vinegar or lemon juice, into the milk. Both processes cause the milk to increase in acidity, giving it a sour taste, and to congeal. When the milk congeals, it hinders the growth of any unfavorable bacteria in it, thus making it safe to consume.”

Meanwhile, spoiled milk is milk that has gone bad, either because it’s well past its printed date, or because it was accidentally left unrefrigerated. It can go bad within just two hours outside the fridge, Maeng says, noting that this is a common food storage mistake to avoid.

If you happen to pour spoiled milk into your cereal, smoothie, or protein shake, and gulp it down, you may get food poisoning, depending on how much you consume.

“Typically, if you ingest enough spoiled milk, it can take a toll on your gastrointestinal tract,” Sonpal says. Your symptoms may include vomiting, cramping, and diarrhea for a period of time from hours to days, he says.

If you only have a sip or two, Maeng says that it’s perfectly possible not to experience any adverse reaction.

If you don’t experience any symptoms, there’s nothing to do. You’re fine.

Mild cases of food poisoning usually pass on their own in due time. But if you do get sick after gulping down a glass, it can’t hurt to go to your doctor’s office just in case. And Sonpal recommends making sure you’re staying hydrated so your kidneys don’t suffer.

If you’re trying to stay hydrated but you keep vomiting, you might be experiencing more severe symptoms, says Sonpal. If this is the case, you should go to urgent care or your doctor’s office so they can keep you hydrated with IV fluid.

Although cow’s milk is better known to spoil, plant-based alternatives (like soy milk, oat milk, and almond milk) can go bad, too. You should always pay attention to your milk’s label, smell, and appearance — whether it’s dairy or an alternative — before consuming it. That being said, alt-milks tend to last a lot longer than cow’s milk, especially when left unopened. Ultra-filtered milk is also more shelf-stable than regular unopened cow’s milk, thanks to the filtration process and pasteurization it goes through. Still, you’ll want to consume it within 7 to 14 days.

• Drinking spoiled milk can lead to uncomfortable gastrointestinal symptoms like vomiting, cramping, and diarrhea, so it's best to avoid accidentally consuming it by regularly checking the smell and appearance of your milk.
• Symptoms from drinking spoiled milk can be mild and self-limiting, but staying hydrated is crucial; if you experience severe symptoms such as persistent vomiting, seek prompt medical attention.
• Both dairy and dairy-free milks can spoil, so it’s important to keep an eye on labels and properly refrigerate them.
• Expiration and best-by dates can vary depending on local regulations, so it's advisable to consider smell, taste, and color changes beyond just the labeled date.