A hydrogen breath test measures hydrogen (and often methane) in exhaled air after ingestion of specific sugars to detect abnormal bacterial fermentation in the gut. It’s used to diagnose conditions such as small intestinal bacterial overgrowth (SIBO) and carbohydrate malabsorption, including lactose or fructose intolerance. Elevated or early rises in these gases indicate bacterial overgrowth or impaired sugar absorption.

A positive hydrogen breath test means excess bacterial fermentation of carbohydrates in your gut, suggesting lactose or fructose malabsorption, small intestinal bacterial overgrowth (SIBO), or rapid transit. Your clinician may confirm diagnosis, recommend dietary changes (eg, low‑FODMAP or lactose restriction), run further tests, or prescribe antibiotics/prokinetics for SIBO. Follow up with a gastroenterologist or dietitian for tailored treatment and monitoring.

Hydrogen breath testing can be worthwhile if you have unexplained bloating, gas or diarrhea and clinicians suspect lactose/fructose malabsorption or SIBO. It's noninvasive and low risk, and can guide dietary or antibiotic therapy. Limitations include false positives/negatives, strict pre-test preparation, and variable accuracy for SIBO—results should be interpreted with clinical history and other tests before treatment.

A positive H2 (hydrogen breath) test is typically defined as an increase in breath hydrogen of ≥20 parts per million (ppm) above baseline within 90–120 minutes after ingesting the test sugar. This rise indicates bacterial fermentation of unabsorbed carbohydrate, suggesting small intestinal bacterial overgrowth or carbohydrate malabsorption. Concurrent methane measurement and clinical correlation often help confirm the diagnosis.

Herbal antimicrobials (oregano oil, berberine, allicin/garlic, neem), dietary strategies that “starve” bacteria (low‑FODMAP, specific carbohydrate or elemental diets), prokinetic measures to improve gut motility (ginger), hydration and treating underlying causes (motility disorders, anatomical problems) can reduce SIBO naturally. Always consult a clinician first—herbs and restrictive diets can interact with medications or be inappropriate for some people.

Hydrogen breath testing costs vary widely by country and setting. Private clinics often charge roughly $100–$300 (about £80–£250), while prices in India commonly run ₹800–3,000. Public health systems frequently offer the test without direct charge when clinically indicated. Final cost depends on test type (glucose, lactulose), facility, laboratory fees and whether insurance covers it.