What should you know about types of lactose intolerance?

Primary lactose intolerance develops when the intestine gradually makes less lactase, the enzyme that breaks down lactose in milk and some dairy foods. Secondary lactose intolerance follows damage or inflammation in the small intestine, such as after an illness or another digestive condition; it may improve when the underlying problem heals. Congenital lactose intolerance is rare and begins from birth because lactase activity is very low.

Undigested lactose passes into the colon, where bacteria ferment it and draw in water. This can cause bloating, abdominal pain, rumbling, gas, or diarrhoea after dairy. The amount tolerated varies, and symptoms can overlap with other digestive conditions. Lactose intolerance is different from a milk allergy, which involves the immune system.

Keep a food and symptom diary, then discuss a structured reduction or reintroduction plan rather than removing every dairy food indefinitely. Some people tolerate small portions with meals, yoghurt, or hard cheese better than a large glass of milk. Lactose-free alternatives or lactase products may help some people.

Protect calcium and vitamin intake when reducing dairy. Nutrition counselling can help choose suitable alternatives, especially for children, pregnancy, or restrictive diets. Food intolerance testing may be considered when the history is unclear, but results need to be interpreted alongside symptoms.

Arrange an assessment for persistent diarrhoea, weight loss, blood in stool, night-time symptoms, fever, ongoing abdominal pain, or symptoms that continue despite avoiding lactose. Seek urgent help for swelling of the lips or tongue, breathing difficulty, faintness, or widespread hives after dairy, as these suggest an allergic reaction rather than lactose intolerance.

Ask which form is possible, whether another bowel condition could explain the symptoms, how to test tolerance safely, and how to maintain calcium and vitamin intake during a trial of lactose reduction.