Lactose Breath Test

The lactose breath test is a simple, non-invasive test that measures hydrogen and methane gases in your breath after drinking a lactose solution. If your body cannot properly digest lactose (the sugar found in milk and dairy products), bacteria in your gut ferment it and produce these gases, which are then detected in your breath.

This is the gold standard test for diagnosing lactose intolerance. It helps differentiate between lactose intolerance and other causes of bloating, gas, diarrhea, and abdominal discomfort. Knowing your lactose tolerance level allows your doctor to recommend precise dietary adjustments rather than unnecessary complete dairy avoidance.

1. You provide a baseline breath sample by blowing into a collection bag
2. You drink a measured lactose solution (usually 25–50g dissolved in water)
3. You breathe into a collection bag every 15–30 minutes for about 3 hours
4. The gases in each sample are measured by a specialized analyzer
5. A rise in hydrogen or methane above baseline confirms lactose malabsorption

About 3 hours

• ✓Fast for 12 hours before the test (water only)
• ✓Avoid antibiotics for at least 4 weeks before the test
• ✓Avoid high-fiber foods the day before
• ✓Do not smoke or exercise vigorously on the morning of the test
• ✓Inform your doctor about all medications you are taking

• •The test is completely painless — just breathing into bags
• •You will need to stay in the clinic during the test (about 3 hours)
• •Some patients may experience bloating, gas, or diarrhea during the test — this is normal and expected if you are lactose intolerant
• •Results are discussed with you on the same day