What is the difference between lactose maldigestion and lactose intolerance?

There is a difference between these two situations.

In both cases (lactose maldigestion and intolerance), only a fraction of lactose is digested. Non-digested lactose enters the colon.

For some individuals, the bacterial fermentation of non-digested lactose in the colon results in one or many symptoms such as bloating, diarrhea, and flatulence. This is called lactose intolerance. Thus, lactose intolerance is lactose maldigestion that results into one or many of these symptoms.

Moreover lactose intolerance concerns very few people, whereas lactose maldigestion concerns 70-75% of the world population.

Sources:

Adolfsson et al. Am J Clin Nutr 2004; 80: 245-56.

Misselwitz et al. United European Gastroenterol J 2013; 1: 151-9.

Szilagyi et al. Can J Gastroenterol Hepatol 2015; 29: 149-56.