There’s a pretty good chance you know the feeling: a threatening rumble in your gut that comes after an extra scoop of ice cream or a particularly milky latte. With it begins your torturous wait for tummy issues like bloating, gas, and gotta-go sprints to the bathroom to subside. And every time you’re left wondering whether your belly’s reaction to dairy means you’ve become a little (or a lot) lactose intolerant.

The likely answer? Well, probably, considering more than two thirds of people worldwide develop some degree of lactose intolerance in their lifetime, according to the National Institute of Health (NIH).

Here’s how it happens: Dairy contains a sugar molecule called lactose that needs to be broken down in your digestive system by an enzyme called lactase, explains Niket Sonpal, M.D., gastroenterology fellow at Lenox Hill Hospital in New York City. When you don’t have enough lactase enzymes in your system, you can’t digest that lactose—and boom, you’re lactose intolerant. “[That lactose] is then taken up by the bacteria in the gut, which causes it to kind of ferment and produce a lot of gas,” Sonpal says.

Some people are born without any ability to produce lactase enzymes, so they spend their entire lives lactose intolerant, says Sonpal. (A lifetime without Ben & Jerry’s Chubby Hubby? Let’s all take a minute to pray for those unfortunate souls.) But what about the adults who suddenly find themselves struggling with dairy?

Basically, everyone’s production of the lactase enzyme declines over time—but how much it declines varies from person to person. “Depending on their genetic makeup, lifestyle, and other factors, everyone’s individual lactose intolerance is different,” says Sonpal. Some people may lose such an inconsequential amount of lactase that they can continue to enjoy dairy without problems for their entire lives, while others may lose so much that even a splash of half-and-half sends their tummy into panic mode.

To learn your true level of lactose intolerance, you can take a quick test at your doc’s office. You’ll consume some dairy and then breathe into a special bag that can measure your ability to digest the lactose you consumed based on the particles in your breath.

But you can also get a general idea of whether dairy is an issue for you by running a little experiment at home, which Sonpal dubs “Lactose and Chill.” Simply eat a dairy-heavy meal (get some cheese and a glass of milk in there) for dinner one night and monitor how you feel. The next night, eat a dairy-free meal and compare your gut reactions (heh).

Quick note: If both meals wreak havoc on your stomach, your issue may be a condition like irritable bowel syndrome, not lactose intolerance, Sonpal says. (People with IBS deal with frequent digestive distress involving anything from bloating to constipation to diarrhea.)

Related: 4 Possible Reasons Why Your Stomach Is Killing You All The Time

But if going ham on dairy does, in fact, leave you gassy, uncomfortable, or running to the bathroom, it’s time to change your diet, says says Keri Gans, R.D.N., author of The Small Change Diet.

“Some people, even with lactose intolerance, can tolerate small amounts of lactose,” she says. So if your belly symptoms weren’t too terrible, you might be okay to enjoy hard cheeses like cheddar (which are naturally lower in lactose), or a bit of milk in your coffee.

But if a glass of milk messes you up bad, you’re best off eliminating dairy from your diet completely. You’ll just need to make sure you get enough calcium and vitamin D, the two primary nutrients you miss out on without dairy in your life, Gans says. Look for plant-based milks that are fortified with calcium and vitamin D, and load up on green leafy vegetables, she suggests. (You may also want to consider a supplement to make sure you’re getting enough of these bone-supporting nutrients.)

When you just can’t avoid dairy (we all need pizza sometimes!), you can try taking a lactose supplement before your meal to help your body deal.