What To Know About Hydrogen Breath Tests

Medically Reviewed by Minesh Khatri, MD on September 14, 2023
4 min read

A hydrogen breath test can help determine if you have one of a few conditions that can affect your digestive health. It may tell you if you have too much bacteria in your gut, if you are lactose intolerant, or if you are fructose intolerant.

Breath tests used for medical purposes were known even in ancient Greece. Hippocrates, whom many call the "father of modern medicine," noted conditions that brought about changes in the smell of someone's breath. He created breath tests to diagnose them. 

Hydrogen breath tests have been in use since the 1970s. Scientists first designed them to diagnose lactose intolerance.

These tests work by measuring levels of hydrogen and possibly methane in your breath. Your body will produce unusual levels of hydrogen or methane if:

Since most people typically have very little hydrogen in their breath, an "unusual level" of hydrogen covers a lot of ground. Then there is a small percentage of the population, fewer than 2% of people, who never produce any hydrogen or methane in their breath. Unless you're one of those people, a hydrogen breath test can be an easy, noninvasive, and cost-effective way to measure your digestive health.

Your doctor may recommend this type of test if you have any of the following:

There are a few different types of hydrogen breath tests. Which one you receive depends on the condition your doctor is trying to diagnose.

Depending on which test you're taking, your doctor may ask you to eat a lower-carbohydrate diet for a few days. They will also let you know if it is safe to take your usual medications before this test. You shouldn't smoke for two hours before the test.   

Typically, you shouldn't take any antibiotics for four weeks before taking one of these tests. Nor can you get a breath test within four weeks of receiving a colonoscopy.  

Lactose breath test. Lactose is a sugar found in milk. Many people have difficulty digesting it, and it gets more difficult as they age. A small number of people are born without the ability to digest milk products. 

To take a lactose breath test, you'll first drink a beverage with lactose. Then your doctor will measure the hydrogen output in your breath at regular intervals throughout your digestion process.

If your body can't digest the lactose, the bacteria in your gut will break it down instead. This will lead to a greater amount of hydrogen on your breath than usual.

Fructose breath test. Fructose is a natural sugar present in many fruits and vegetables. Some people can develop an intolerance to it throughout their lives, while others are born without the enzyme needed to digest fructose.

If you receive a fructose breath test, your doctor will first measure the hydrogen levels in your breath. Then you will drink a beverage containing fructose. Your doctor will track the hydrogen levels in your breath for the next three hours. If there is more hydrogen in your breath than before you drank the beverage, you may have fructose intolerance.

SIBO breath test. An overgrowth of bacteria in the small intestine leads to uncomfortable symptoms such as bloating, gas, and diarrhea. 

To test for SIBO, you first drink a sugary beverage. Then you breathe into a special device that will tell your doctor whether too much hydrogen is in your breath. If there is, SIBO may have put it there.  

But this is a test for carbon dioxide, and the bacteria is in your stomach.

H. pylori breath test. Helicobacter pylori is a type of bacteria that can cause chronic inflammation of the digestive system. It may lead to problems such as ulcers or cancer. 

You must not eat for one hour before a breath test for H. pylori. The test is done with a tube inserted in your nose and attached to a breath analyzer. Your doctor will test your breath before giving you a special solution to drink. They'll then take another reading after you've drunk the solution. The level of carbon dioxide they find in your breath at this point may show you may have this bacteria.

It's important not to take bellyache and gas for granted. Let your doctor know if these conditions happen to you on a regular basis.