7 Lactose Intolerance Symptoms You Shouldn’t Ignore

Updated: Jan. 21, 2024

A stomachache after a glass of milk is probably nothing, but if you feel sick every time you eat dairy, you might be facing a bigger problem.


1. You regularly experience bloating and gas

You know pretty quickly when the frozen yogurt you ate an hour ago isn’t digesting correctly; you’ll feel it in your puffed-out abdomen. Joel B. Mason, MD, a professor of medicine and nutrition at Tufts University, says all of these lactose intolerance symptoms can be the result of a deficiency of the enzyme lactase, which typically breaks down the two types of sugar in each lactose molecule so they can be easily absorbed into the intestine. Without lactase, lactose molecules will travel down the intestinal track whole and bacteria will try to break them down through a process of fermentation, which produces a whole lot of extra gas in your abdomen.

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2. Your belly is in pain, and making sounds

Without lactase, your body’s attempt at breaking down lactose by itself can draw a lot of water into your intestine, in addition to gas in your gut, which are symptoms of lactose intolerance. The result is an unfortunate combination of diarrhea, cramps, and the sound of gurgling or rumbling in the belly, also known as borborygmi. According to eMedicineHealth.com, sometimes the diarrhea of someone who is lactose intolerant will also appear foamy, the result of all of the extra gas and fluid sloshing around in the gut.

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3. You feel nauseous after eating dairy

There are different degrees of lactose intolerance, according to Chicago-based registered dietitian Karen Raden, RD; some individuals experience more extreme symptoms of lactose intolerance than others. In the worst cases, a lactase deficiency can cause someone to feel the need to vomit shortly after they consume a dairy product. “Gas in the intestine inflates it like a balloon, inducing a vomiting response,” says Dr. Mason. This reaction is relatively rare, according to Raden, but if it’s regularly occurring to you when you eat milk products, it’s probably a sign of a lactase deficiency.

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4. Your ethnicity has higher rates of lactose intolerance

We all need lactase to digest our mother’s milk as infants, but evolution didn’t automatically equip us to keep consuming lactose into adulthood. Humans’ ability to digest lactose in adulthood didn’t develop until about 5,000 years ago, among cattle herders in northern Europe, for whom the ability to digest milk was especially useful, according to the New York Times. Though genetics that allow for the presence of lactase in the body have spread in large portions of the Caucasian and East African populations, East Asian, South Asian, and other African populations have much higher incidences of adults experiencing symptoms of lactose intolerance, according to Dr. Mason.

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5. You’re not sick with something else

The cramping and diarrhea of lactose intolerance resemble the symptoms of other types of inflammatory bowel diseases, including Crohn’s disease and irritable bowel syndrome, according to Healthline.  While lactase deficiencies are more common in those with Crohn’s disease than those without, and Raden says someone can have both irritable bowel syndrome and lactose intolerance, it’s important to remember the key distinguishing characteristic of lactose intolerance symptoms: they only occur after someone consumes milk-containing products. To test your own lactose intolerance symptoms, try not consuming dairy for a while and see if the bloating, gas, and stomach pain go away. If they don’t, you might be facing a different digestion-related issue.

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6. You’re not an infant anymore

There are several types of lactose intolerance; some lactase deficiencies are present from birth, some develop as the result of damage to the small intestine, and most develop during childhood or later. Rarely is someone born without any lactase at all. The most common form of lactose intolerance develops sometime after age 2, according to the National Institute of Diabetes and Digestive and Kidney Diseases. Approximately 30 million adults in the United States will develop lactose intolerance symptoms by age 20, according to the U.S. National Library of Medicine.

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7. Your test results are positive

If you suspect you have any lactose intolerance symptoms, it’s time to visit the doctor’s office and ask about getting a hydrogen breath test. When lactose is digested by bacteria in a lactase-deficient individual, the bacteria release hydrogen into the bloodstream that your doctor will measure in your breath. If your lactose intolerance diagnosis is official, you can start finding other ways to consume the vitamin D and calcium you’ll miss from not eating dairy, or pair dairy with a lactose supplement like Lactaid to help your body digest it.

Reader's Digest
Originally Published in Reader's Digest