Acute or temporary lactose intolerance

Undigested lactose then reaches the large bowel, where fermentation and extra water can cause wind, bloating, cramps and loose stools after dairy foods.

Lactase sits on the lining of the small intestine and breaks down milk sugar for absorption. Gastroenteritis or another condition that irritates this lining can temporarily reduce the enzyme. Some people instead notice a gradual, longer-term decline, so the timing and medical history matter.

Symptoms are linked to the amount of lactose eaten and personal tolerance. They usually involve the bowel rather than hives, facial swelling or breathing difficulty. Those allergic-type features suggest a different reaction to food proteins and require separate assessment.

Keep a short record of dairy foods, portion sizes, symptom timing and bowel changes. A temporary reduction in high-lactose foods may clarify the pattern, followed by cautious reintroduction as the gut recovers. Many people tolerate smaller portions, lactose-free products or some fermented and hard dairy foods better than a large serving of milk.

Avoid excluding every dairy product for an extended period without considering calcium, protein and vitamin intake. A GP or dietitian can check for alternative causes, advise suitable replacements and decide whether a supervised elimination and reintroduction or breath testing is appropriate.

Arrange medical review for persistent diarrhoea, repeated symptoms without a clear food link, weight loss, fever, waking at night with symptoms or blood in the stool. Seek urgent help for severe or worsening abdominal pain, fainting, marked dehydration, vomiting that prevents fluid intake, facial or tongue swelling, wheezing or breathing difficulty.

Ask whether recent infection or another bowel condition could explain reduced lactase, how long to trial dietary changes, and how to reintroduce lactose. Discuss whether testing would change management, which nutrients need attention, and which symptoms would warrant investigation for coeliac disease, inflammatory bowel disease or another diagnosis.