Lactose is the natural sugar in milk. To digest it, the small bowel needs an enzyme called lactase. Most adults in Asia make less lactase after childhood, so undigested lactose reaches the large bowel, where bacteria ferment it and produce gas.
Symptoms
Symptoms usually start 30 minutes to a few hours after milk or dairy, and depend on how much you had:
- Bloating and passing more wind
- Cramping abdominal pain
- Loose stools or diarrhoea
- Rumbling in the stomach
Lactose intolerance is not dangerous and does not damage the bowel. It is different from a milk allergy, which is an immune reaction that can cause rash, swelling or breathing difficulty, usually in children.
Finding out
- The simplest test is to avoid milk and dairy for two weeks, then try a glass of milk and see whether the symptoms come back
- A hydrogen breath test can confirm it
- If symptoms continue without dairy, other causes such as IBS or chronic diarrhoea are looked for
What you can do
- Most people can manage a small amount, such as a little milk in coffee, especially with food
- Yoghurt and hard cheeses contain much less lactose and are often fine
- Choose lactose-free milk, or take lactase drops or tablets with dairy
- If you cut down on dairy, get calcium from other foods, such as calcium-set tofu, small fish eaten with the bones (ikan bilis, sardines), green leafy vegetables, or calcium-fortified soy milk
When to see a doctor
See a doctor if you have diarrhoea that lasts more than a few weeks, blood in the stool, weight loss, or symptoms that started for the first time later in life. These need checking for other causes.
General information only. Reviewed by Dr Chia Chung King, 2026-11-13. Book a consultation.