Developing lactose intolerance: what to know

Lactase is an enzyme that breaks down lactose, the natural sugar in milk. When less lactose is digested in the small intestine, it reaches the colon, where bacteria ferment it and draw in fluid. This can lead to bloating, abdominal pain, gas, or diarrhoea after dairy. The amount and timing of symptoms vary, and some people tolerate small portions or yoghurt better than other products. Lactose intolerance is different from a milk allergy, which involves an immune reaction and may cause hives, swelling, vomiting, or breathing difficulty.

Note which foods cause symptoms, the portion eaten, and how soon symptoms begin. Do not remove every source of dairy for a long period without a plan, because calcium and vitamin D intake may fall. A clinician or dietitian can help you try a structured reduction and reintroduction, choose lactose-free alternatives, and check whether another digestive problem is contributing. Food intolerance testing may be considered in selected situations, but a careful history is often central. Lactase products may help some people, although product choice and use should be discussed with a professional.

Arrange medical review for persistent diarrhoea, weight loss, blood in stool, fever, nighttime symptoms, dehydration, or pain that is severe or progressive. Seek emergency help for facial or throat swelling, widespread hives, wheezing, or trouble breathing after milk, since these features suggest an allergic reaction rather than lactose intolerance. Sudden severe abdominal pain also needs prompt assessment.

Could another condition explain my symptoms? Should I try a supervised lactose reduction? How can I protect calcium and vitamin D intake? Would testing help? Which symptoms would suggest milk allergy or another urgent problem?