Lactose intolerance occurs when the digestive system can't fully digest lactose — the sugar found in milk. Instead of being digested and absorbed, the lactose stays in the gut and causes the symptoms of lactose intolerance. For example, the lactose may be metabolised by bacteria to produce acids and gases that lead to discomfort. Many people with lactose intolerance can often tolerate small amounts of lactose.

Symptoms of lactose intolerance are gastrointestinal. They include feeding and bowel problems such as wind, diarrhoea, bloated tummy, tummy aches and cramps, tummy rumbling and feeling sick. These symptoms can also be a sign of cow’s milk allergy.

However, because cow’s milk allergy involves the immune system, babies who are allergic to cow's milk protein may also show allergy symptoms like an itchy rash, wheezing, or runny noses and coughs. These skin and respiratory symptoms aren't seen in lactose intolerance because this condition doesn't involve the immune system.

Lactose intolerance may occur temporarily, for example after having a tummy bug. In these cases it will usually resolve in the short term. Other cases of lactose intolerance may be lifelong, such as in those born with a primary lactose intolerance or those who develop it as they get older. Primary lactose intolerance is uncommon before 2–3 years of age.

Speak to your doctor if you suspect that your child may have lactose intolerance.