How to test for lactose intolerance

Lactose intolerance is a common condition that involves the inability to break down and digest lactose, a type of sugar typically found in milk and other dairy products. There are several ways to test for lactose intolerance.

Yes, there are several methods of testing for lactose intolerance.

The most common lactose intolerance test is called the hydrogen breath test. This test will be ordered by your healthcare provider. Your provider will likely review the preparation and test instructions with you prior to the procedure. This usually involves: 

• Avoiding certain medications, like laxatives and antibiotics, prior to testing
• Fasting and avoiding heavy exercise before the test
• Breathing into a special balloon or collection tube for a baseline sample
• Drinking the test liquid, which contains a premeasured amount of lactose
• Taking breath samples at set times specified by the test, typically every 30 minutes over several hours

The hydrogen breath test measures how much hydrogen gas is in your breath. Normally, very little hydrogen gas is found in the air we exhale, but if your body has difficulty breaking down lactose, those levels will rise. Test results showing an abnormally high level of hydrogen gas in your breath samples may indicate lactose intolerance.

A stool acidity test may be used to evaluate lactose intolerance in infants and young children. This test is typically performed by a pediatrician or a specialist. The test analyzes the stool to see if it contains higher than expected levels of glucose, lactic acid and other fatty acids. Elevated amounts of these substances may indicate lactose intolerance.

Another way to test for lactose intolerance is through a series of blood tests that measure changes in your blood sugar after you consume a liquid that contains lactose. When lactose is broken down and absorbed by the intestines, blood sugar levels normally rise over the next two hours. If this doesn't happen, it may indicate lactose intolerance.

If you suspect you have lactose intolerance, talk with your healthcare provider. They can review your symptoms, discuss appropriate testing options, and help determine whether lactose intolerance or another condition may be causing your digestive symptoms.

Clinically reviewed and updated July 2026.