What condition prevents the digestion of lactose?

Lactose intolerance is the condition that prevents the normal digestion of lactose. Lactose is the main sugar in milk, and the small intestine normally breaks it into glucose and galactose using the enzyme lactase.

When the body produces too little lactase, undigested lactose passes into the colon. Gut bacteria ferment it, producing gas, while the unabsorbed sugar draws water into the intestine. This can cause bloating, cramps, flatulence, nausea, and diarrhea, usually within 30 minutes to two hours after consuming dairy.

Most people develop the common primary form as lactase production naturally declines after childhood. Secondary lactose intolerance can follow intestinal infections or diseases such as celiac disease or Crohn's disease. Rare congenital forms begin at birth. The condition is not the same as a milk allergy, which is an immune reaction to milk proteins rather than a difficulty digesting sugar.

Tolerance varies widely: many affected people can consume small portions, especially with meals. Lactose-free products and lactase supplements can help manage symptoms.