Explanation

Lactose intolerance is a problem your body has with absorbing lactose. Lactose is a type of sugar found in milk, so you actually become intolerant of milk. To be absorbed, lactose must be broken down into two smaller sugars by an enzyme called lactase in your small intestine.

If there is not enough lactase or none at all, the lactose doesn't get broken down and you get problems like too much gas and diarrhoea. You can become lactose intolerant if you have coeliac disease and your small intestine becomes really inflamed and damaged.