Lactose intolerance

What is lactose intolerance?

Lactase is the enzyme that splits lactose, the sugar in milk. If lactose is not split, it reaches the large bowel and ferments. That can cause gut symptoms. Three terms sit on this one page and they are not interchangeable:

• Lactase deficiency (hypolactasia) — the small bowel makes little lactase.
• Lactose malabsorption — undigested lactose reaches the colon. This can be silent.
• Lactose intolerance — malabsorption plus symptoms after lactose.

Malabsorption is not the same as intolerance. A test that shows lactose is not fully absorbed does not, by itself, mean you have lactose intolerance.

NHS Inform says secondary lactase deficiency is the most common UK cause, especially in babies and children, after gastroenteritis or with conditions such as coeliac disease, Crohn’s disease, or ulcerative colitis. Adult primary lactase non-persistence is more often noticed in people of Asian or African-Caribbean descent. Congenital lactase deficiency is very rare (NHS). Guts UK states that 8 in 100 people might have lactose intolerance in the UK. How common it is beyond that figure is unknown.

Not cow’s milk allergy, and not coeliac disease

Lactose intolerance is not cow’s milk protein allergy (CMA), not dairy allergy, and not coeliac disease. Intolerance is a dose-dependent digestive problem with lactose. CMA is an immune reaction to milk protein and can include anaphylaxis. Coeliac disease is an autoimmune reaction to gluten. Lactose-free cow’s milk still contains milk protein and is unsafe for CMA.

Common symptoms

NHS information (reviewed 8 July 2026) describes symptoms that start minutes to hours after lactose:

• Abdominal pain
• Bloating
• Wind
• Diarrhoea or constipation
• Nausea

Symptoms are dose-dependent. Extra-gut symptoms are non-specific and are not a diagnosis. Red-flag features need a GP. Anaphylaxis is allergy, not lactose intolerance — call 999.

Common patterns

• Temporary lactose intolerance after gastroenteritis is common and often settles.
• Secondary lactase deficiency with coeliac disease or IBD often improves when the underlying condition is treated.
• Hard cheese and yoghurt are often better tolerated than a glass of milk.
• Lactose in medicines is usually far below a symptom threshold. SPS (2025) notes that medicines are unlikely to exceed 2 g of lactose a day, and that a typical symptom threshold is about 12 g of lactose (about 250 ml of milk). Medicines’ lactose is not a routine explanation for everyday symptoms.

Overlapping conditions

Lactose is a FODMAP, so IBS and lactose intolerance can sit together. Coeliac disease and IBD can cause secondary lactase deficiency. Post-infectious IBS, SIBO, bile acid malabsorption, and microscopic colitis are diarrhoea differentials. Distinguishing them is a clinician’s job. This page is not a self-diagnosis tool.

Lactose, FODMAPs, and fructose

Lactose is one FODMAP. A low-FODMAP diet should only be used with a dietitian, for a planned trial, not as a lifelong internet protocol. Fructose malabsorption is a different sugar issue. This is not a fructose page.

Research and tests

NHS pathways include an elimination trial, a hydrogen breath test, and sometimes a blood glucose test. NICE CG61 says hydrogen breath tests are not needed to confirm IBS. Misselwitz and colleagues (Gut, 2019) report that most people who malabsorb lactose still tolerate at least 12 g as a single dose, and more when it is taken with food. That matches the SPS threshold figure. Direct-to-consumer genetic tests sold as a US-style “diagnosis” are not a UK clinical diagnosis.

Approaches people discuss

Lactose intolerance is not a milk-protein allergy and not coeliac disease. Most people do better reducing lactose than cutting every dairy food forever.

• Established Reduce lactose rather than a lifelong zero-lactose diet for most people. Lactose-free dairy, or fortified plant alternatives, can help. A dietitian-led exclusion and reintroduction is the gold-standard way to confirm the link. Misselwitz et al. (Gut, 2019) report that most people who malabsorb lactose still tolerate at least 12 g as a single dose, and more with food — matching the SPS threshold. Sources: NHS lactose intolerance; NHS Inform; SPS; Misselwitz et al. Gut 2019.
• Established Do not cut dairy from a child's diet without a GP or dietitian. Long-term over-restriction risks calcium, vitamin D, and bone health. Sources: NHS; Allergy UK.
• Established Lactase tablets help some people. They are not a cure and they do not treat cow's milk allergy (CMA). Sources: NHS; Allergy UK.
• Limited Commercial IgG food panels, hair analysis, kinesiology, and Vega testing. Guts UK says there is no evidence for these. The NHS does not recommend them. Direct-to-consumer genetic tests sold as a diagnosis are not a UK clinical diagnosis. Sources: Guts UK; NHS; Allergy UK.

Community insights

Anecdotal themes:

• IgG kits, hair tests, and kinesiology are widely sold as “food intolerance tests”. They are not a diagnosis of lactose intolerance.
• People often treat lactose intolerance as if it were a milk-protein allergy. Lactose-free cow’s milk is still milk protein.
• Hard cheese and yoghurt come up often as better tolerated than milk — that matches NHS-style practical advice, not a personal protocol from this site.
• Cutting all dairy from a child’s diet without clinical support is a common worry in community threads, because bone health is easy to undermine.