Lactose intolerance

Synonyms: Lactose intolerant

Medical Specialties: Family practice, Gastroenterology

Clinical Definition

Lactose intolerance is the inability to digest lactose, a milk sugar, usually due to an intestinal deficiency of the enzyme lactase.

In Our Own Words

When people suffer with the digestive condition lactose intolerance, they are—to varying degrees—unable to digest lactose, which is a form of sugar found in dairy products and many other processed foods. Lactose intolerance is not an allergy to milk. Rather, it is the effect of reduced activity of lactase, an enzyme in the small intestine that breaks down lactose. While most babies are “pros” at lactose digestion, many adults lose this ability with age.

Relevant Conditions
  • Celiac disease
  • Crohn’s disease
  • Gastritis
Side Effects
  • Gas and bloating
  • Diarrhea
  • Nausea
Share this article
  • Cleveland Clinic. “Lactose Intolerance” last reviewed August 12, 2010. Accessed July 2013.
  • Ohio State University, Wexner Medical Center. “Digestive Disorders: Lactose Intolerance.” Accessed July 2013.
  • Merck Manual. “Carbohydrate Intolerance.” August 2012. Accessed July 2013.
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