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Question: What causes lactose intolerance?

Answer: Two factors contribute to lactose intolerance: lactose malabsorption and gut sensitivity. Lactose malabsorption is the most important factor. It’s the inability to break down and absorb lactose in your small intestine that leads to lactose later entering your large intestine and triggering symptoms.

1. Lactase deficiency: Your small intestine needs a specific enzyme, called lactase, to break down lactose into smaller molecules that it can absorb. Most people naturally produce lactase in their small intestines during infancy to help digest breast milk. Most people begin to make less of it as they grow up. If you don’t have enough lactase, you won’t be able to digest lactose. Some people produce more or less lactase than others. But technically, the majority of people worldwide have lactose malabsorption due to lactase deficiency. Only certain populations continue to produce lactase into adulthood.

2. You and your gut: This is where your gut sensitivity factors in. We all consume things from time to time that we can’t fully digest. Certain dietary fibers and sugars go straight through our digestive systems to feed the bacteria living in our guts. Most of us tolerate a little of this to some extent, without overwhelming symptoms. But everyone is a little different. Our genes, intestinal health, sensitivities and diet all factor in. Your unique gut microbiome — the different types of bacteria living in your colon — may process lactose differently from someone else’s. Your symptoms will tell you how much lactose you can tolerate.

(Source: Cleveland Clinic, 31 Jan 2026)

Source Link: https://my.clevelandclinic.org/health/diseases/7317-lactose-intolerance