Lactose intolerance occurs when the small intestine does not produce enough lactase. Lactase is required to digest lactose in the diet. Lactose intolerance generally develops in individuals as they age. People tend to become lactose intolerant around their teenage years, or during adulthood.
If your parents have lactose intolerance, it is very likely that you may too suffer from same. Lactose Intolerance runs in our genetics. Lactose intolerance can also be brought on by infection of intestine (gastroenteritis, rota virus infection), chemotherapy, surgery, or from the avoidance of dairy products for a prolonged period of time.