Lactose intolerance
Difficulty digesting lactose, the sugar in milk, because the gut makes too little of the enzyme lactase. Undigested lactose causes bloating, wind, cramps and diarrhoea after dairy. It is common, harmless in itself, and managed by limiting lactose rather than with medication.
What it is
Lactose intolerance is the inability to fully digest lactose, the main sugar in milk and dairy products. Lactose is broken down in the small intestine by an enzyme called lactase; when there is not enough lactase, undigested lactose passes into the large bowel where gut bacteria ferment it, producing gas and drawing water in. The most common form appears as lactase production naturally declines after childhood, which is very common worldwide and varies a lot by ancestry. Lactose intolerance can also be secondary — a temporary loss of lactase when the gut lining is damaged by an infection (gastroenteritis), coeliac disease, or Crohn's disease — and improves if the underlying problem is treated. Symptoms come on from about 30 minutes to a couple of hours after eating dairy and depend on how much lactose was taken: bloating, abdominal cramps, excessive wind, and diarrhoea are typical. It is important to know that lactose intolerance is not the same as a milk allergy, which is an immune reaction and can be dangerous. Lactose intolerance itself is not harmful to the body; the issue is symptoms and quality of life, and it is managed by adjusting how much lactose is eaten.
Key lab markers
- No routine blood marker confirms it — the diagnosis is often clinical, from symptoms and improvement when lactose is reduced.
- Hydrogen breath test — the usual formal test; measures breath hydrogen after a lactose drink.
- Fecal elastase and coeliac serology — used to look for other causes of similar malabsorption symptoms.
- Tests to find a secondary cause — such as coeliac disease or Crohn's, if a new intolerance appears.
Symptoms
- Bloating and a feeling of fullness after dairy
- Excessive wind (flatulence)
- Abdominal cramps and pain
- Diarrhoea, often loose and watery
- Nausea, and sometimes rumbling in the gut
- Symptoms roughly 30 minutes to 2 hours after milk or dairy
- Severity depends on the amount of lactose eaten
When to discuss with a doctor
Lactose intolerance is common and, in itself, not dangerous — the goal is comfort and good nutrition. If dairy reliably brings on bloating, wind, cramps and diarrhoea, it is reasonable to see whether reducing lactose helps, and many people can still tolerate small amounts, hard cheeses, yoghurt or lactase-treated products. It is worth seeing a doctor to confirm the picture and, importantly, to rule out conditions that can mimic or cause it, such as coeliac disease or inflammatory bowel disease — especially if symptoms are new, severe, or come with weight loss, blood in the stool, or symptoms unrelated to dairy. Because cutting out dairy affects calcium and vitamin D intake, doing so thoughtfully matters. Mediora.AI can show malabsorption and coeliac markers alongside your symptom pattern to help distinguish lactose intolerance from other causes; the diagnosis and dietary plan are best made with your doctor.