Adult onset lactose intolerance

Undigested lactose reaches the large bowel, where bacteria ferment it and draw in fluid. This can cause bloating, wind, cramps or loose stools after dairy. The amount that triggers symptoms varies, and lactose intolerance is different from an allergy to milk proteins.

Lactase production commonly falls after childhood, so foods that once caused no trouble may become harder to digest. Symptoms can also appear temporarily after an intestinal infection or alongside a condition that affects the small-intestinal lining. The timing after food, portion size and whether symptoms recur help a clinician assess the pattern.

Lactose intolerance commonly presents with abdominal discomfort, bloating and diarrhoea after lactose-containing food. These symptoms have other possible causes, so their presence alone does not establish the diagnosis.

Keep a brief food-and-symptom diary, noting the dairy product, portion and what happened afterwards. A clinician may suggest a structured lactose reduction followed by reintroduction, or a breath test when the cause remains uncertain. Avoid cutting out every dairy food without a plan, because tolerance differs between products and unnecessary restriction can reduce calcium, protein and vitamin intake.

Smaller portions, lactose-free alternatives or lactase products may help some adults. A dietitian can identify tolerated foods and help replace nutrients if restriction is needed.

Arrange a clinical review if symptoms persist, repeatedly interrupt meals, begin after an intestinal illness, or continue even when lactose is avoided. Seek prompt care for blood in the stool, ongoing vomiting, unexplained weight loss, fever, dehydration, severe or worsening abdominal pain, or symptoms that wake you from sleep.

Breathing difficulty, facial or throat swelling, widespread hives or collapse after milk exposure may indicate an allergic emergency rather than lactose intolerance; call emergency services immediately.

Ask whether your symptom pattern fits lactose intolerance, whether another digestive problem should be checked, and whether a supervised elimination trial or breath test would be useful. Discuss which dairy foods you might still tolerate and how to maintain adequate calcium and vitamin D if your diet changes.