Irritable bowel syndrome (IBS) is a gastrointestinal disorder characterized by a group of symptoms that typically occur together. These symptoms may include:

IBS is thought to be related to problems with how your brain and your gut work together.

Lactose intolerance is a digestive disorder that occurs when you can’t digest lactose, a natural sugar found in dairy products. People with lactose intolerance don’t produce enough of an enzyme called lactase, which is essential for digesting lactose. When you consume dairy, lactose intolerance can cause a variety of symptoms similar to those of IBS.

Their underlying causes, risk factors, and treatments are different, however.

IBS and lactose intolerance can sometimes have similar symptoms, such as diarrhea, bloating, and gas. However, these two disorders aren’t related. Symptoms of lactose intolerance only occur when you consume dairy. This isn’t true for IBS.

IBS is considered a functional gastrointestinal (GI) disorder. Symptoms of IBS aren’t as clear-cut. Some people with IBS have constipation. Some have diarrhea. Others go back and forth between the two.

Unlike lactose intolerance, which is triggered by eating dairy products, IBS symptoms can have many triggers, including certain types of foods or stress and anxiety.

Dairy can also be a trigger food for someone with IBS, but this doesn’t necessarily mean the person is intolerant to lactose.

Lactose intolerance is very common. Roughly 68 percent of people worldwide have or will develop lactose intolerance in their lifetime. While most people are born with enough lactase to digest milk, the amount of lactase a person makes may decrease gradually over time.

Risk factors for lactose intolerance include:

IBS is more common in women than in men. Genetics may also play a role, but there is still a lot that scientists have to learn about the cause of IBS.

Factors that can increase your chance of having IBS include:

  • having a family member with IBS
  • a history of stress or trauma
  • having a severe infection in your digestive tract

Many symptoms of lactose intolerance can also be symptoms of IBS, though there are a few key differences.

Lactose intoleranceIBS
Excessive gas (flatulence)Excessive gas (flatulence)
Stomach crampsStomach cramps
Nausea and vomitingConstipation
Symptoms occur 30 minutes to 2 hours after eating or drinking a dairy productConstipation alternating with diarrhea

It’s possible to have both IBS and lactose intolerance. This is mainly because the two conditions are both fairly common. Lactose intolerance occurs in nearly two-thirds of people worldwide and in over one-third of people in the United States. Studies estimate the prevalence of IBS is somewhere between 10 and 15 percent of people in the U.S.

While people with IBS often report lactose intolerance, researchers haven’t found any conclusive evidence to suggest a link between the two.

Lactose intolerance often gets worse as you age and your body loses the ability to produce lactase. Still, the severity of symptoms is usually relative to the amount of lactose you consume.

IBS is more difficult to diagnose than lactose intolerance. A doctor may want to rule out lactose intolerance or other gastrointestinal disorders, such as celiac disease, while testing for IBS. It takes longer to diagnose IBS than it does to diagnose lactose intolerance.

Diagnosing lactose intolerance

You may be able to self-diagnose lactose intolerance by avoiding dairy products (like milk, cheese, and ice cream) and seeing if your symptoms improve. After 1 to 2 weeks, if you consume some milk and your symptoms return, it’s very likely you have lactose intolerance.

A doctor can also order a test known as a lactose breath test to confirm a diagnosis.

Diagnosing IBS

A doctor may need to order a variety of tests to make a diagnosis, and some of these tests may be used to rule out other conditions. They will also ask about your diet, family medical history, and symptoms, and look for a certain pattern in these symptoms.

The diagnostic process for IBS may involve:

  • blood testing to rule out the possibility of celiac disease (wheat allergy)
  • taking a stool sample to check for parasites or blood that could indicate an infection
  • an X-ray of your intestines to check for possible blockages
  • a colonoscopy to rule out the possibility of colon cancer
  • a CT scan of the pelvic region to help rule out problems with the pancreas or gallbladder
  • a lactose breath test

Once these other conditions are ruled out, a doctor can make a diagnosis of IBS if you’ve had symptoms consistent with IBS for at least 3 months over the previous year.

Treatment for both IBS and lactose intolerance will involve making changes to your diet. IBS treatment will likely also involve making changes to your lifestyle and possibly taking medications.

Treating IBS

You may be able to control symptoms of IBS by making changes to your diet and lifestyle. These changes include:

  • eating more fiber
  • avoiding gluten
  • adapting to a special eating plan known as a low FODMAP diet
  • increasing physical activity
  • reducing stress

When you’re experiencing symptoms of IBS, such as diarrhea or constipation, a doctor may prescribe medications like:

You may have to try a few treatments to see what works best for you.

Treating lactose intolerance

The main treatment for lactose intolerance is to avoid foods containing lactose.

Though you may be able to tolerate a small amount of lactose at a time, you should generally try to avoid the following:

  • cow’s milk
  • goat’s milk
  • cheese
  • ice cream
  • yogurt
  • butter
  • sour cream
  • whey protein

You’ll have to check food labels of other products to make sure they don’t contain lactose. Cookies, cakes, chocolate, bread, cereal, and many sauces and gravies or prepared foods contain lactose. You can replace milk products with dairy milk alternatives like cashew or almond milk. There are also milk products available with the lactose removed.

You can also try taking lactase enzyme supplements before consuming dairy to reduce the chances of having symptoms.

Both IBS and lactose intolerance aren’t associated with serious medical consequences, but both can impact your quality of life.

If you’re experiencing gastrointestinal symptoms, such as diarrhea, stomach cramping, gas, bloating, or constipation on a regular basis that can’t be explained easily by eliminating dairy from your diet, see a doctor for a proper diagnosis.

IBS is a disorder of bowel function, while lactose intolerance is related to an enzyme needed to digest dairy. These two disorders aren’t related but have very similar symptoms. It’s also possible to have both of these conditions at the same time. If you’re experiencing gastrointestinal problems often, including stomach pain, diarrhea, or constipation, see a doctor for more testing.