Is It IBS or Lactose Intolerance?

Medically Reviewed by Minesh Khatri, MD on March 17, 2024
3 min read

Irritable bowel syndrome (IBS) and lactose intolerance can seem similar. The symptoms they cause are nearly identical. But there are distinct differences in why they happen and how you handle them.

If you have lactose intolerance, it’s because your body doesn’t digest one specific type of food: the sugar in milk. If you have IBS, on the other hand, many things can be behind your symptoms. You can have both conditions at the same time, but they are two separate problems.

IBS and lactose intolerance can both cause:

IBS can also cause constipation. You might have mucus in your stool or feel like you can’t completely empty your colon. Symptoms can change over time and flare up, get better, or disappear.

Along with the other symptoms, lactose intolerance can cause nausea. You usually start to feel bad between 30 minutes and 2 hours after you eat milk or other dairy products.

It’s not clear what causes IBS. Some doctors think it happens when the muscles around the colon don’t work properly to move waste along. A problem with the signals between the brain and the nerves in the gut may also play a role. It might also happen when someone is very sensitive to triggers like some foods or stress.

Although the cause is still a mystery, doctors do know some things that can raise your risk for IBS, including:

  • Your genes
  • Infections in your intestines
  • Long-term stress or emotional trauma

Lactose intolerance is better understood: The body can’t digest the sugar in milk, called lactose. It happens when your body doesn’t make enough of the enzyme lactase, which the gut uses to break down lactose. It’s not a harmful condition, but it can keep you from getting the right amount of important nutrients like calcium and vitamin D, which most people get from dairy products.

The problem can run in families. You’re also more likely to have it if you have another digestive disease, like:

  • Ulcerative colitis
  • Crohn’s disease
  • Celiac disease

Only a doctor can tell if your symptoms come from IBS or lactose intolerance. They usually diagnose IBS based on the symptoms you describe. For lactose intolerance, you’ll need to give a little more information, such as:

  • Your family history
  • A physical exam
  • A hydrogen breath test. Undigested lactose in your body gives off high levels of hydrogen. During the test, you drink a beverage that has lactose, then blow air into a special bag. A lab tests your breath to look for the gas.

IBS symptoms can come and go, but it’s a condition you’ll have for the rest of your life. There is no cure for it. But you can use a few different strategies to manage how you feel. Changes to your diet and tools to handle stress may help ease your symptoms. Medications like anti-diarrhea drugs or laxatives can make you feel better, too. It’s important to work with a doctor to find the approach that works for you.

There is also no cure for lactose intolerance, but it usually helps to avoid milk, cheese, and other dairy foods. Some people with the condition can handle small amounts of them, and others have to cut them out completely. Your doctor or dietitian can help you figure out the right diet and suggest supplements that may help. There are lactase enzyme replacements available that can be taken with food, but they have varying degrees of benefit.