Why it happens
Babies make plenty of lactase, but in many people it declines after weaning. That's the global norm; persistent lactase is common mainly in people of Northern European descent. Undigested lactose ferments in the colon and causes gas, bloating, and diarrhea. A milk allergy is an immune reaction with hives or breathing trouble, a completely different problem.
Managing it and getting calcium
Most people with lactose intolerance can handle about 12 grams of lactose (roughly a cup of milk) at once, especially with a meal. Aged cheeses and yogurt are lower in lactose, and lactose-free milk or lactase pills help. If you cut back on dairy, get calcium from fortified foods, canned fish, and leafy greens.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- Can you build up tolerance?
- Your lactase won't increase, but small regular amounts may let gut bacteria adapt and ease symptoms.
- How is it diagnosed?
- A hydrogen breath test is common, though many people just test whether symptoms improve when they cut lactose.
Sources reviewed: 2026-10-26
References
- Misselwitz, B., et al. (2019). Update on lactose malabsorption and intolerance. Gut, 68(11), 2080–2091.
- National Institute of Diabetes and Digestive and Kidney Diseases. Lactose Intolerance. NIDDK.
- Storhaug, C. L., Fosse, S. K., & Fadnes, L. T. (2017). Country, regional, and global estimates for lactose malabsorption in adults. The Lancet Gastroenterology & Hepatology, 2(10), 738–746.