Milk, infant formula, breast milk and dairy products all contain a type of sugar called lactose. Those who suffer from lactose intolerance are unable to properly digest this type of sugar in their bodies.

A key difference between the symptoms of colic and those of lactose intolerance is that the lactose intolerant baby suffers from diarrhoea. The osmotic pressure generated by lactose and lactic acid in the stomach produces an influx of water leading to a swollen abdomen and acidic diarrhoea.