What Are the Symptoms of Lactose Intolerance?

Medically Reviewed By Adrienne Seitz, MS, RD, LDN
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The symptoms of lactose intolerance include abdominal pain, bloating, gas, and diarrhea. Some people may be able to prevent or lessen the symptoms of lactose intolerance. However, others may need to avoid products containing lactose completely. The number and severity of symptoms you experience can depend on how much lactose-containing foods you consume.

Read on to learn more about the symptoms of lactose intolerance, including their causes, treatments, and how to prevent them.

What are the symptoms of lactose intolerance?

A closeup of a hand holding a glass of milk that is spilling
Juan Moyano/Stocksy United

The most common symptoms of lactose intolerance include:

  • abdominal pain or cramping
  • bloating
  • gas
  • stomach growling or rumbling
  • nausea
  • vomiting
  • diarrhea

Less common symptoms can include:

The Canadian Society of Intestinal Research notes that symptoms typically appear anywhere from 30 minutes to 2 hours after consuming lactose.

Researchers also note that lactose intolerance is rare in children under the age of 5. The condition most often affects adolescents and young adults.

What causes lactose intolerance symptoms?

The symptoms of lactose intolerance occur when your body is unable to process lactose, a sugar found in milk products. In many people, the small intestine produces an enzyme called lactase, which breaks down lactose into components the body can absorb.

In people with lactose intolerance, also called lactose malabsorption, the body does not produce enough lactase to break down the sugar. The undigested lactose then travels into the colon, where bacteria break it down and produce gas and fluid.

This excess gas and fluid are what cause lactose intolerance symptoms.

Learn more about the risk factors and complications of lactose intolerance.

How do you treat lactose intolerance symptoms?

According to the National Institute of Diabetes and Digestive and Kidney Diseases, symptoms of lactose intolerance are often manageable. You can manage symptoms by avoiding or limiting your intake of products that contain lactose. These include milk, cheese, yogurt, and other milk products.

Some people may also benefit from taking lactase supplements to help their bodies break down lactose. These supplements are available as tablets or drops.

Lactose intolerance can sometimes result from an injury to the small intestine. In these cases, medical treatment to address the injury may increase your tolerance for lactose.

Some people may be able to tolerate more lactose in their diet by slowly increasing the amount they consume. However, this may not be an option for everyone.

How do doctors diagnose lactose intolerance?

To diagnose lactose intolerance, your doctor will start by assessing your medical history and performing a physical examination.

If they suspect lactose intolerance, they may recommend avoiding products containing lactose for two weeks. If your symptoms return after adding lactose back into your diet, this may be a sign you have lactose intolerance.

Your doctor may also suggest testing to help them make a diagnosis. Tests can include:

  • Hydrogen breath test: After fasting overnight, you will breathe into a bag to create a baseline for the test. Then, you will drink a small amount of milk sugar and breathe into the bag again. A hydrogen content that rises more than 20 parts per million (ppm) indicates lactose intolerance.
  • Stool acidity test: A stool test may reveal a lower-than-usual pH due to unabsorbed lactose.
  • Milk tolerance test: After drinking milk, your doctor will monitor your blood sugar levels. If the levels do not increase, it could indicate that your body is not breaking down lactose.

Other frequently asked questions

Here are a few other common questions about lactose intolerance. These answers were reviewed by Adrienne Seitz, M.S.

What are the 4 types of lactose intolerance?

The four types of lactose intolerance are primary, secondary, congenital, and developmental. In the primary type, your lactase activity declines with age. The secondary type results from an injury to the intestinal lining. This is usually caused by infections, inflammation, or medications.

Congenital lactose intolerance is rare and is present at birth. The developmental type appears in premature infants whose intestines are underdeveloped, and usually improves over time.

What triggers lactose intolerance?

Lactose intolerance can be triggered by a few factors. In some cases, genetics can influence your body’s ability to break down lactose. In other cases, an injury to the small intestine can hinder the production of lactase.

What foods should you avoid if you have lactose intolerance?

If you have lactose intolerance, you may need to limit or avoid intake of foods containing lactose. These include milk and milk products such as cheese and yogurt.


Lactose intolerance symptoms commonly include gas, diarrhea, bloating, and abdominal pain. Some people may also experience nausea, vomiting, and stomach cramps.

You may be able to manage symptoms by avoiding or limiting your intake of products containing lactose. Lactase supplements may also help you digest milk products if your body does not produce enough on its own.

Talk with your doctor about ways to manage your lactose intolerance symptoms.

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Medical Reviewer: Adrienne Seitz, MS, RD, LDN
Last Review Date: 2022 Nov 16
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