People with lactose intolerance cannot digest the sugar (lactose) in milk because they have symptoms after eating or drinking dairy products. This type of intolerance is usually harmless, but its symptoms can be very uncomfortable. This is the result of lacking lactase, which is produced in the small intestine and the symptoms usually begin 30 minutes to two hours after consuming dairy foods.
These symptoms include diarrhoea, nausea, abdominal cramps, bloating and gas. However, most people with this problem can manage the condition without having to give up all dairy foods.