What Is Lactose Intolerance?

Lactose intolerance is a condition that results in uncomfortable digestive symptoms after you consume foods or drinks that contain lactose—or a sugar that is naturally found in dairy products. These uncomfortable digestive symptoms, such as bloating, gas, and diarrhea, are caused by lactose malabsorption, which means your small intestine cannot digest or breakdown all of the lactose you consume.

Approximately 65% of people in the world are lactose intolerant. However, this condition is most common in African Americans, Hispanics/Latinos, and Asians and least prevalent in people of European descent.

Some people are born with lactose intolerance while others develop the condition as they age. Your treatment options will vary based on how frequently you experience them and their severity. Fortunately, not everyone who is lactose intolerant will have to completely eliminate dairy. In fact, research indicates that most people can tolerate some lactose in their diet—especially if they eat it with other foods.


When your small intestine does not make enough of the digestive enzyme lactase, you can develop lactose intolerance. Lactase is responsible for breaking down the lactose in the foods you eat so your body can absorb the nutrients. 

There are four types of lactase deficiency that could potentially lead to lactose intolerance:

  • Lactase non-persistence: Lactase non-persistence is the most common type deficiency. People who have this condition experience a decline in lactase production over time. And while the condition may be inherited, they may not show signs of lactose intolerance until late adolescence or even adulthood.
  • Secondary lactase deficiency: This type of deficiency is the result of an injury to the small intestine from conditions such as Crohn's disease or Celiac disease. Once the underlying condition is treated, the lactose intolerance may improve. Rotavirus and giardia also can cause damage to the surface of the small intestine resulting in temporary lactose intolerance.
  • Developmental lactase deficiency: Developmental lactase deficiency is usually the result of premature birth. When a baby is born too soon, the small intestine may not make enough lactase to digest milk sugar causing lactose intolerance. But as they get older, the small intestine usually makes more lactase and the condition subsides.
  • Congenital lactase deficiency: While this form of deficiency is extremely rare, congenital lactase deficiency occurs when the small intestine produces little or no lactase enzyme from birth. This condition is usually inherited and is present from the time you are born.

Lactose Intolerance Symptoms

When you have lactose intolerance, you will likely experience symptoms 30 minutes to 1 to 2 hours after consuming dairy products. The severity of your symptoms are influenced by how much lactose you consumed. In other words, having a bowl of ice cream or a glass or milk will affect you differently than cheese sprinkled on your salad.

Your lactose intolerance is also influenced by how much lactase you have in your body and how long it takes the food you ate to leave your small bowel. The most common signs and symptoms of lactose intolerance include:

  • Diarrhea
  • Bloating
  • Abdominal pain
  • Nausea and vomiting
  • Stomach rumbling
  • Gas

Older research indicates that lactose intolerance also can potentially cause headaches, muscle pain, joint pain, mouth ulcers, urinary symptoms, and loss of concentration. Though, these symptoms are not very common.

What Causes Lactose Intolerance?

Lactose intolerance is caused by lactose malabsorption, which occurs when your small intestine makes low levels of the enzyme lactase and can't digest all the lactose you eat or drink. When you have a lactase deficiency, your body doesn't produce enough lactase in order to digest the lactose in your foods and drinks.

Risk Factors

While some people inherit the condition, you also can be at risk as you age as well as if you have certain medical conditions. Here are some of the more common risk factors for lactose intolerance.

  • Having a parent with lactose intolerance
  • Getting older
  • Having gastroenteritis
  • Developing a bowel disease like Crohn's disease or ulcerative colitis
  • Receiving chemotherapy
  • Taking antibiotics
  • Being born prematurely

How Is Lactose Intolerance Diagnosed?

Finding the root cause of a food intolerance like lactose intolerance is not an easy process, especially because the symptoms mimic those of other common gastrointestinal and bowel disorders. That said, there are several ways to diagnose lactose intolerance.

Hydrogen Breath Tests

Conducting a hydrogen breath test (HBT) is currently considered the gold standard for diagnosing lactose intolerance. This is primarily due to the test's high sensitivity and specificity as well as the fact that it is an inexpensive test that is simple to use and non-invasive.

The test is based on the measurement of hydrogen exhaled every 30 minutes after taking lactose (usually 25 grams which is equivalent to about 500 milliliters of milk). When the hydrogen level in the exhaled air is 20 parts per million or greater than the baseline, the test is positive for lactose intolerance.

Elimination Diets

Sometimes a healthcare provider will have you follow an elimination diet where you avoid anything that contains lactose to see if your symptoms improve. They also may ask you to keep a journal of what you eat and any symptoms you experience. These two options will help your healthcare provider determine if you have lactose intolerance or not.

Lactose Tolerance Test

The lactose tolerance test evaluates your blood sugar levels after you drink a lactose solution. If your blood sugar doesn't rise significantly, it's a sign that you are lactose intolerant. This lack of elevation occurs because your body can't absorb the sugar building blocks if the lactose isn't broken down. During this test, your blood sugar levels are measured regularly over a two hour period while watching for symptoms like diarrhea or cramps.

Treatments for Lactose Intolerance

While there’s no known cure for lactose intolerance, there are a number of things you can do to treat the condition. The first approach is to limit the amount of lactose you consume in a day's time. That said, it is important to note that it is rarely advised that you completely eliminate foods that include lactose.

Aside from the fact that dairy products contain important vitamins and minerals—like vitamin D, vitamin B12, magnesium, and calcium—most research indicates that people with lactose intolerance can consume about 12 grams of lactose, which is equivalent to about 1 cup of milk. Meanwhile, studies show that 18 grams of lactose can be tolerated when consumed with other foods or spread out in small amounts throughout the day.

There also is some limited evidence that gradually exposing your body to lactose could help your body adapt to it. In fact, one study indicates that consistent exposure could prompt your body to produce some lactase and reduce symptoms. Even though studies are limited, the results show promise.

How to Prevent Symptoms of Lactose Intolerance

Although there is no way to prevent yourself from developing lactose intolerance, there are things you can do to mitigate the symptoms. Aside from limiting dairy products in your everyday diet, you also can take lactase supplements to help you digest the lactose you consume. However, it is important to note that the effectiveness of these products vary widely.

There also is some limited evidence that probiotics and prebiotics may reduce symptoms of lactose intolerance. However, not all probiotics have the same impact. Bifidobacteria and Lactobacillus, which are often found in probiotic yogurts and supplements, have been shown to be the most effective.

You can even try using lactose-free products which are made lactose-free by removing the lactose during the manufacturing process. One well-known dairy brand is Lactaid, but plant-based milks—like cashew milk, almond milk, soy milk, and oat milk—are naturally lactose free. There are also a number of non-dairy products such as coconut yogurt, cashew cheese, and more. Talk to a healthcare provider to determine which products are right for you.

Comorbid Conditions

Having lactose intolerance also can put you at risk for other conditions as well. For instance, there is some evidence that lactose intolerance is related to everything from osteoporosis to depression. Here is a closer look at several of the more studied comorbid conditions.

  • Osteoporosis: Not getting enough calcium in your diet puts you at risk for low bone density or osteoporosis. For this reason, it would make sense that people who are limiting their dairy intake would be at a higher risk for osteoporosis. While some studies have shown this to be the case, other studies have had conflicting results.
  • Celiac disease: People with lactose intolerance are more likely to have celiac disease. In fact, one study found that people with a positive lactose breath test had a high prevalence of celiac disease.
  • Mental health conditions: Several older studies indicate that there could be a connection between those with lactose intolerance and different mental health conditions. For instance, one study found that lactose intolerance may impact the availability of serotonin. For this reason, researchers recommend investigating whether or not people with depression also have lactose intolerance.

Living With Lactose Intolerance

If you have been diagnosed with lactose intolerance, you likely experience uncomfortable digestive symptoms when you eat dairy products. Fortunately, there are things you can do to address your condition and reduce your symptoms.

Aside from limiting how much dairy you eat, you can also try spacing its consumption out throughout the day as well as eat dairy with other foods to minimize your reaction. There also are supplements you can take to help your body digest the lactose you eat as well as products that are made without lactose.

Finding out how much dairy you can eat during a day as well as whether or not lactase supplements will work for you will take some trial and error. While this may take some time, with the help of your healthcare provider, you should be able to find an approach that works for you. They also can help monitor important vitamins and minerals—such as vitamin D, calcium, vitamin B12, and magnesium—to ensure you are getting the nutrients you need.

Dietary supplements are minimally regulated by the FDA and may or may not be suitable for you. The effects of supplements vary from person to person and depend on many variables, including type, dosage, frequency of use, and interactions with current medications. Please speak with your healthcare provider or pharmacist before starting any supplements.

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Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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