Lactose Intolerance Symptoms & Diagnosis

Symptoms

Symptoms of lactose intolerance generally begin within two hours of consuming milk or other dairy products. The severity of symptoms depends on how much lactase your body produces and how much lactose you eat.

Symptoms include:

Nausea
Cramping
Bloating
Abdominal rumbling sounds
Gas
Diarrhea
Loose stools

Diagnosis

The doctor will ask about your symptoms and medical history and perform a physical exam. Often he or she will recommend a two-week trial period of eating no milk or milk products. If symptoms subside, you will be asked to consume milk products again. If milk causes symptoms to recur, you will be diagnosed with lactose intolerance.

Your doctor may also order some tests, including:

Lactose tolerance test—measures the amount of glucose (simple sugar that is created from lactose) absorbed two hours after drinking a high-lactose liquid, indicating how well the body is digesting lactose

Hydrogen breath test—measures how much hydrogen is exhaled after drinking a high-lactose liquid

Stool acidity test—measures lactic acid in the stool for infants and small children

Biopsy of the small intestine—only performed in rare cases, this involves removing and testing a sample of tissue to confirm lactase deficiency

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition. Copyright © 2025 EBSCO Publishing All rights reserved.