Lactose is the naturally occurring sugar in animal milks. When ingested, lactose has to be split into its components glucose and galactose which are then absorbed. This can only happen when sufficient lactase is present in the gut.
Lactose intolerance is the inability to digest lactose. In the gut, lactose needs to be broken down by the enzyme lactase. People with lactose intolerance lack or do not produce enough lactase, and undigested lactose remains in the gut causing tummy discomfort, diarrhea and bloating.
An easy way to resolve this is to cut out milk and dairy products - and thereby lactose - from your diet and replace them with dairy free alternatives such as those made by Alpro.
Further information can be found on http://www.nutrition.org.uk/nutritionscience/allergy/lactose-intolerance
An allergy involves a reaction by the immune system, while a food intolerance does not - although sometimes the symptoms can seem similar. In the case of dairy allergy, the cow's milk protein is the allergen provoking the immune system to react, which in some people can be extremely severe.
Whether someone has lactose intolerance or a milk allergy, Alpro products provide a great alternative to dairy, as they're all naturally lactose and dairy free.