Lactose is a sugar found in milk, but is also present in dairy products and food items made with milk derivatives. Lactose intolerance is different from milk allergy. Milk allergy is a situation where under which the body is allergic to milk proteins and not milk sugar. A person having a situation of lactose intolerance may not only have to avoid milk and milk products such as ice cream, but also other processed foods including whey, milk powder and so on.
People with lactose intolerance cannot metabolize lactose properly because their digestive system produces an enzyme called lactase in a very small amount.