Lactose Intolerance: Causes, Symptoms, and Treatment

Many delicious foods contain dairy in some way, shape, or form—and those dairy-filled dishes may lead to symptoms including pain or gas for those with lactose intolerance.

To avoid the pain that is associated with a diet including dairy, there are many who are eliminating dairy from their diet, among other health benefits.

What Is Lactose Intolerance?

Lactose intolerance is when your body is unable to digest lactose—a type of sugar found in milk—and the lack of digestion can cause symptoms. This condition comes from not having enough lactase—an enzyme necessary to break down lactose.

Lactase works in your small intestine to break down sugars from dairy. However, if there is not enough lactase to break down the lactose in your food and drink, those sugars move through your system to your colon. Bacteria in your colon break down lactose and cause the symptoms of lactose intolerance.


Lactase can be produced by cells in your small intestine. However, if these cells are injured or have genetic changes, they may create little to no lactase leading to lactose intolerance and the associated symptoms.

Lactase production is controlled by a gene named LCT. As such, mutated LCT genes create lactase that cannot digest lactose. In rare cases, people can be born with LCT gene mutations and have lactose intolerance from birth. More commonly, people develop lactose intolerance as they age because their body stops using the LCT gene to make lactase. Lactose intolerance can often run in families because of these genetic causes.

Injuries to the small intestine can also cause lactose intolerance. Some examples of injuries include gastrointestinal conditions like Crohn's disease and celiac disease. Medications, surgery, and radiation therapy can also cause damage to the small intestines.

However, if the damage to your small intestine has a chance to heal, you may regain your ability to digest lactose.


Symptoms of lactose intolerance can start within two hours after ingesting dairy products and include:

  • Abdominal pain
  • Bloating
  • Diarrhea
  • Gas
  • Nausea
  • Stomach "growling" or rumbling sounds
  • Vomiting

Diarrhea, gas, and abdominal pain—are the most common symptoms, Rabia de Latour, MD, gastroenterologist and assistant professor of medicine at NYU Langone Health, told Health. These symptoms are caused by bacteria in your colon breaking down undigested lactose, creating extra fluid and gas that your body then expels.

These listed symptoms vary depending on the person and their digestive speed. As mentioned earlier, the symptoms typically start within two hours after consuming a dairy product.

Diagnosis and Testing

Healthcare providers can diagnose lactose intolerance using a few different techniques. "Most of the time, it's a clinical diagnosis," Dr. de Latour said. When patients say something like, "Every time I have milk in my coffee, I get these symptoms," the statement signals to healthcare providers that their patients could have lactose intolerance.

During the diagnosis process, you may also be asked to keep a food diary. Writing down what you eat might make you more aware of what causes your stomach to hurt. Other methods of diagnosis include using a scope to examine your intestines or lactose tolerance tests.

Some lactose intolerance tests include the hydrogen breath test and the glucose blood (blood sugar) test. Both tests are fasting tests—meaning you would avoid eating or drinking 8–12 hours before your appointment. You'll also be asked not to do the following things before your test:

  • Use antibiotics
  • Do strenuous exercise
  • Smoke

During the test, you will drink a liquid with lactose, and the hydrogen in your breath or your blood sugar is measured for several hours. High levels of hydrogen and no increases in blood sugar indicate that you are lactose intolerant.


The good news is that even if you have lactose intolerance, the condition is easily manageable. One option is to limit or eliminate lactose-containing foods from your diet. You can also try lactase products that can help you digest dairy products. If your lactose intolerance is due to a small intestine injury, you can work with your healthcare provider to treat that injury.

According to Dr. de Latour, lactose intolerance is "not a super dangerous disease to have—just inconvenient."

A Quick Review

You may be lactose intolerant if you experience symptoms such as diarrhea, gas, and abdominal pain after consuming dairy products like cheese and milk. Lactose intolerance is the inability to digest lactose which is caused by a genetic mutation or change in gene activity.

A healthcare provider may diagnosis you with lactose intolerance after noticing your symptoms with a food diary or by examining your intestines for injury. Their treatment is usually a recommendation to cut out—or cut back on—dairy products in your diet. This will decrease or eliminate your symptoms.

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  1. National Library of Medicine. Lactose intolerance.

  2. National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms & causes of lactose intolerance.

  3. National Library of Medicine. Lactose tolerance tests.

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