Hydrogen Breath Test

One simple test, many helpful results!

Woman blowing into a hydrogen breath test machine.

A simple hydrogen breath test can tell all kinds of things about your health!
© Can Stock Photo

A hydrogen breath test can be a useful diagnostict tool.

It’s often used to determine what kinds of problems might be going on in your bowels. Although some people think of this test as a lactose intolerance test, it has many other uses. I’ll describe some in a minute, but first of all…

What is a hydrogen breath test?

At the end of the day, a hydrogen breath test is really a test for undigested food, or bacteria in the wrong place in your bowels.

Here’s how a hydrogen breath test works. After not eating anything for a while (usually 8 to 12 hours or so) you drink a fluid containing a certain kind of sugar. The kind of sugar depends on what your doctor is testing for.

Here’s what happens if your body can’t digest this test sugar:


  1. The sugar gets consumed by bacteria in your colon (anaerobic or non-oxygen breathing bacteria).
  2. This bacteria gives of hydrogen as it digests the sugar.
  3. Some of the hydrogen gets absorbed into the blood stream and gets exhaled through the lungs.
  4. The doctor can tell if you have a problem be seeing how much hydrogen there is in your breath.

What can the doctor tell from a hydrogen breath test?

This test is almost always used to find out if you are:

  • Lactose intolerant
  • Fructose intolerant
  • Have bacteria in your small intesting that doesn’t belong there.
  • Have an h. pylori stomach infection (which can lead to ulcers and other problems)

A hydrogen breath test can also be used to see if food is moving too fast through the small intestine.

Why is all this so important?

Hydrogen breath test and small bowel bacteria:

THe small intestine isn’t supposed to have too much bacteria in it. The colon or large bowel is full of bacteria though. If you have an overgrowth of bacteria in your small bowel it may be the cause of your IBS symptoms. This may be one reason why Rifaximin antibiotic treatment helped IBS sufferers in a test study.

The Hydrogen breath test and lactose intolerance:

A box of many kinds of sugars.

There are many kinds of sugars. Fruit sugars, lactose (milk sugar), cane sugar. A hydrogen breath test can help you find out if they are causing you health problems.
© Can Stock Photo

If your body can’t break down lactose (milk sugar) then you’ll end up with all the classic IBS symptoms. Three quarters of the people in the world are lactose intolerant. Lactose intolerance is also more common as people age. A hydrogen breath test for lactose intolerance can help to determine if that’s your real problem.

Hydrogen breath test and fructose intolerance:

Fructose is fruit sugar. Some people can’t digest it very well at all.

Other people can digest small amounts of fructose, but larger amounts give them cramps, diarrhea, and other IBS symptoms.

If your fructose hydrogen breath test comes back positive, you could be fructose intolerant. If so, you can eliminate this problem food from your diet (though it’s difficult).

H. Pylori, ulcers, and the hydrogen breath test:

When I was having a lot of reflux (severe heartburn) my gastroenterologist gave be a hydrogen breath test. He later told me that he used it to determine that I had h. pylori. This bacteria can lead to ulcers. The treatment was a special antibiotic.

If my doctor hadn’t found it, I could be dealing with ulcers now.

High Speed Intestines:

If food moves too fast through your small intestine, it can cause problems in your colon (your large intestine). For instance, if a bunch of partially digested food ends up in your large intestine, the bacteria there will devour the sugars and other components.

This can lead to gas, cramping, diarrhea, bowel spasms and many other IBS symptoms.

In Conclusion…

A hydrogen breath test can help you and your doctor find out about foods that may be making you sick. You may be one sweet drink away from finding out.

Read more about IBS medical help in the the IBS medical help section.

Find out more about food intolerance on the food intolerance page or in the food intolerance section.

Or return to the Homepage.

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