Lactase is an enzyme that breaks down lactose, a sugar in milk. About 95% of the world's population is lactose intolerant, meaning they can't digest lactose. This limits their ability to get the essential nutrients from milk. Lactase can be derived from the beta-galactosidase enzyme, which is found in almost every living thing. The body can produce lactase when needed, but levels can vary from person to person. Some people can't do anything to help increase their lactase levels, while others may need to take enzyme supplements.