People with lactose intolerance are unable to fully digest the sugar (lactose) in milk. This digestion is brought about by enzyme lactase. Due to absence of lactase,lactose cannot be digested, as a result, people can have diarrhea, gas and bloating after eating or drinking dairy products. The condition, which is also called lactose malabsorption, is usually harmless, but its symptoms can be uncomfortable. A deficiency of lactase — an enzyme produced in your small intestine — is usually responsible for lactose intolerance. Many people have low levels of lactase but are able to digest milk products without problems. If you're actually lactose intolerant, though, your lactase deficiency leads to symptoms after you eat dairy foods.

Most people with lactose intolerance can manage the condition without having to give up all dairy foods. Primary lactose intolerance is the most common type of lactose intolerance. It takes 5 to 6 months from the birth, for the normal production of lactase. From 5 to 6 months onwards lactase production is normal, the from 5 to 8 years onwards levels starts declining. This is seen in most of the asian population. Primary lactose intolerance is genetically determined, occurring in a large proportion of people with African, Asian or Hispanic ancestry.