"Lactose Intolerance" is the inability of body to break down lactose.

Lactose is a  form of sugar that is found in milk or milk products. Lactose is broken down by an engyme named LACTASE produced by the cells linning in the small intestine. By lactase, lactose is converted into galactose. Being absorbed in the bloodstream galactose then goes to liver and being converted into glucose re-enters into bloodstream.