Some people cannot digest milk because their small intestine produces too little lactase, the enzyme that breaks down milk sugar called lactose.
Undigested lactose reaches the large intestine, where bacteria ferment it. This can cause:
Bloating and gas
Stomach cramps
Diarrhoea
Nausea
This condition is called lactose intolerance. It often develops with age and is more common in certain populations.
It is different from a milk allergy, where the immune system reacts to milk proteins such as casein or whey. A milk allergy can cause rashes, swelling, vomiting, breathing difficulty, or a severe allergic reaction.
Many lactose-intolerant people can still tolerate small amounts of milk, yoghurt, hard cheese, lactose-free milk, or lactase enzyme tablets.
