Lactase is an organic molecule that contains both carbon and hydrogen. Of the various groups of organic molecules, lactase belongs to the proteins, which are made up of very long chains of amino acids. Lactase functions as an enzyme, a special kind of protein that facilitates chemical reactions.
Lactase is the enzyme that helps the body break down milk sugar into digestible bits. Without lactase, the body cannot digest milk effectively. This inability is called lactose intolerance, because the problematic milk sugar goes by the scientific name of lactose. Lactase is a very important enzyme because milk is the primary food for all young mammals, including humans, until they have grown enough to consume solid food.