Congenital Lactase Deficiency: A rare genetic condition where infants are born with little to no lactase enzyme, making it difficult to digest milk. 2. Primary Lactose Intolerance: ...

This is called lactase persistence or lactase non-persistence. What has generally been assumed is that if you do not produce the enzyme lactase as an adult, you will be lactose intolerant.

Lactaid is one brand of lactase enzyme. When taken with lactose-containing foods, a lactase replacement allows the body to process those foods normally.