Lactose intolerance is an inability to digest the sugar in milk, called lactose. It’s a common problem that affects up to 68 percent of people.

Normally, your small intestines produce an enzyme called lactase to break apart lactose molecules. If you have lactose intolerance, your body doesn’t produce enough of this enzyme to effectively break down the milk sugar when you consume dairy.

The inability to breakdown lactose leads to symptoms such as:

The symptoms of lactose intolerance are similar to other digestive issues like irritable bowel syndrome (IBS). However, a variety of foods can trigger IBS while lactose intolerance is limited to dairy.

It’s also possible to have a milk allergy, which is different from lactose intolerance. Milk allergies cause an immune response that may lead to more serious symptoms like:

  • shortness of breath
  • throat swelling
  • tingling around your mouth

The symptoms of lactose intolerance usually begin within 30 minutes to 2 hours after consuming dairy and should go away once the dairy you consumed completely passes through your digestive system — within about 48 hours.

Lactose intolerance isn’t usually a serious condition, but it can cause stomach discomfort.

The severity of your symptoms can vary based on the amount of lactose you consume and the amount of lactase your body produces.

All the symptoms of lactose intolerance should resolve within about 48 hours, if not earlier. These symptoms will last for as long as lactose is in your digestive system:

  • Bloating. Bloating is caused by trapped water and gas in your intestines. Bloating pain is often felt around your belly button.
  • Nausea. You may experience nausea within 2 hours of eating dairy if you have lactose intolerance.
  • Diarrhea. Undigested lactose ferments in your gut and leads to increased water retention.
  • Gas. When lactose ferments in your gut, it can lead to a build-up of hydrogen, methane, and carbon dioxide.
  • Pain. Pain in the abdominal region is common for people with lactose intolerance. Pain is usually from trapped gas pushing against the walls of your intestines.

Food intolerances and food allergies can both cause stomach discomfort.

A food allergy causes an immune system reaction that can cause serious symptoms throughout your body, such as throat swelling. Food intolerances are caused by an inability to break down a particular food and usually only cause symptoms that affect your digestive system.

Here’s how long you can expect symptoms of these other digestive problems to last:

  • IBS. Symptoms of IBS can last for days to months at a time.
  • Dairy allergy. Symptoms of a dairy allergy usually start within 2 hours of drinking milk but can be delayed up to 72 hours if milk continues to be consumed.
  • Gluten intolerance. Gluten intolerance is a lifelong issue that flares up shortly after eating gluten and can last days at a time.
  • Alcohol intolerance. People with alcohol intolerance often notice symptoms within 20 minutes of having a drink, and symptoms can last until the alcohol leaves your system.

Lactose intolerance isn’t curable. It’s caused by a deficiency of the enzyme lactase and right now there’s no way to increase your body’s production of this enzyme.

Some people may benefit from taking lactase tablets before a meal containing dairy. However, the tablets don’t work for everybody.

Even though lactose intolerance can be uncomfortable, it’s usually not a serious condition.

If you suspect you’re lactose intolerant, you may want to visit a doctor to rule out other digestive conditions and to get confirmation of your diagnosis. A doctor can test you in one of three ways.

Lactose tolerance test

During a lactose tolerance test, a doctor will take a blood sample and look at your fasting glucose levels. You will then drink a liquid containing lactose. Over the next several hours, the doctor will compare your blood glucose levels to your baseline.

If your glucose levels aren’t elevated, it means that your body isn’t able to break down the lactose into individual sugars and you’re lactose intolerant.

Hydrogen breath test

During the hydrogen breath test, you’ll drink a liquid with a high concentration of lactose. A doctor will then measure the amount of hydrogen in your breath.

If you’re lactose intolerant, the fermented lactose in your gut will release extra hydrogen in your breath.

Stool acidity test

The stool acidity test is usually only used on children who can’t be tested using other methods. The test looks at the acidity of a stool sample to test for undigested lactose in the form of lactic acid.

Lactose intolerance may not be curable, but there are ways you can manage your symptoms.

  • Eat smaller portion sizes. Some people with lactose intolerance can handle a small amount of dairy. You can try eating a tiny amount of dairy and seeing how your body reacts before slowly increasing your portion sizes.
  • Take lactase enzyme tablets. Taking an over-the-counter tablet containing the enzyme lactase before a meal may help you consume dairy. However, the tablets don’t work for all people.
  • Take probiotics. Research suggests that consuming probiotics may help reduce symptoms of lactose intolerance.
  • Eliminate types of dairy. Hard cheeses, butter, and yogurt are naturally lower in lactose than other types of dairy.
  • Try lactose-free products. Many grocery stores sell dairy products that are either lactose-free or with a significantly reduced amount of dairy.

Symptoms of lactose intolerance usually begin between 30 minutes and 2 hours after consuming dairy.

The symptoms last until the lactose passes through your digestive system, up to about 48 hours later.

The severity of your symptoms can be mild or severe depending on how much dairy you eat.

Being lactose intolerant can make it more difficult to get your daily recommended amount of calcium. You may benefit from incorporating more dairy-less sources of calcium into your diet, such as:

  • canned salmon
  • sardines
  • seeds
  • fortified nondairy milk
  • spinach and kale
  • beans and lentils
  • broccoli
  • almonds
  • oranges
  • figs
  • tofu
  • rhubarb