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Lactose Intolerance

Lactose Intolerance: What You Need to Know

Platter of assorted cheeses, which contain lactose.

  • Lactose intolerance is a condition in which an individual is unable to digest lactose, a sugar found in milk and milk products.

  • This condition often runs in families and can be developed by both children and adults.

  • Lactose intolerance is most common in Asian Americans, African Americans, Mexican Americans and Native Americans.

  • Symptoms vary from person to person, but may include: gas, diarrhea, bloating, belly pains and/or nausea.

  • There is no treatment for lactose intolerance, but symptoms can be managed through diet changes.

What is lactose intolerance?

Lactose intolerance happens when your small intestine does not make enough of a digestive juice (enzyme) called lactase. Lactase is needed to break down the lactose in food so it can be absorbed by your body.

People who are lactose intolerant have unpleasant symptoms after eating or drinking milk or milk products. These symptoms include bloating, diarrhea, and gas.

Lactose intolerance is not the same thing as having a food allergy to milk.

What causes lactose intolerance?

Lactose intolerance can happen to children or adults. Here are some common causes of this condition:

  • Lactose intolerance often runs in families (hereditary). In these cases, over time a person’s body may make less of the lactase enzyme. Symptoms may occur during the teen or adult years.

  • In some cases the small intestine stops making lactase after an injury or after a disease or infection.  

  • Some babies born too early (premature babies) may not be able to make enough lactase. This is often a short-term problem that goes away.

  • In very rare cases some newborns can’t make any lactase from birth.

What are the symptoms of lactose intolerance?

Each person’s symptoms may vary. Symptoms often start about 30 minutes to 2 hours after you have food or drinks that have lactose.

Symptoms may include:

  • Belly (abdominal) cramps and pain

  • Nausea

  • Bloating

  • Gas

  • Diarrhea

How severe your symptoms are will depend on how much lactose you have had. It will also depend on how much lactase your body makes.

The symptoms of lactose intolerance may look like other health problems. Always see your health care provider to be sure.

How is lactose intolerance diagnosed?

Your health care provider will talk to you about your past health and family history. He or she will give you a physical exam.

You may be asked not to have any milk or milk products for a short time to see if your symptoms get better.

You may also have some tests to check for lactose intolerance. These may include:

  • Lactose tolerance test. This test checks how lactose is absorbed by your digestive system. You will be asked not to eat or drink anything for about 8 hours before the test. This often means not eating after midnight. For the test, you will drink a liquid that has lactose. Some blood samples will be taken over a 2-hour period. These will check your blood sugar (blood glucose) level. If your blood sugar levels don’t rise, you may be lactose intolerant.

  • Hydrogen breath test. You will drink a liquid that has a lot of lactose. Your breath will be checked several times. High levels of hydrogen in your breath may mean you are lactose intolerant.

  • Stool acidity test. This test is used for infants and young children. It checks how much acid is in the stool. If someone is not digesting lactose, their stool will have lactic acid, glucose, and other fatty acids.  

More Information About Lactose Intolerance from Johns Hopkins Medicine

Woman with stomach pain

5 Foods to Avoid if You Have IBS

While lactose intolerance and irritable bowel syndrome (IBS) are two different conditions, both can cause similar symptoms for individuals who drink milk or eat milk products. In this article, Dr. Linda Lee, a gastroenterologist at Johns Hopkins, explains why.

Read more.

Lactose Intolerance Treatment

There is no treatment that can help your body make more lactase. But you can manage your symptoms by changing your diet.

Lactose intolerance symptoms can be unpleasant, but they won’t hurt you. So try to find dairy foods that don’t cause severe symptoms.

Learn more about living with lactose intolerance by controlling your diet.

When should I call my health care provider?

Call your health care provider if you have trouble managing your symptoms. Some symptoms can be embarrassing. Your health care provider can work with you to help keep them under control.

Key points about lactose intolerance

  • Lactose intolerance is when your body can’t break down or digest lactose. Lactose is a sugar found in milk and milk products.

  • It happens when you don’t have enough of an enzyme called lactase. Lactase breaks down lactose in food.

  • The most common symptoms of lactose intolerance are belly cramps and pain, nausea, bloating, gas, and diarrhea.

  • There is no treatment that can help your body make more lactase.

  • You can manage your symptoms by changing your diet.

Next steps

Tips to help you get the most from a visit to your health care provider:

  • Before your visit, write down questions you want answered.

  • Bring someone with you to help you ask questions and remember what your provider tells you.

  • At the visit, write down the names of new medicines, treatments, or tests, and any new instructions your provider gives you.

  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.

  • Know how you can contact your provider if you have questions.

More Information About Gastrointestinal Conditions in the Health Library

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