Hydrogen breath tests identify whether or not you have lactose intolerance. When lactose (a type of sugar found in certain foods) is not absorbed properly in your small intestine, it moves further down into your large intestine where it then reacts with bacteria to produce an excess of hydrogen gas. This hydrogen gas travels through your bloodstream and into your lungs, leading to higher levels of hydrogen found in your breath. Before your hydrogen breath test, you’ll be given a small amount of lactose and then have your breath measured for hydrogen levels at regular intervals. Hydrogen breath tests for lactose intolerance (and also fructose intolerance) are available at Direct Endoscopy.