Lactose intolerance is an impaired ability to digest lactose, a type of sugar found in milk and other dairy products. During digestion, lactose is broken down into two simple sugars by lactase, an enzyme found in the small intestine. However, if an insufficient amount of this enzyme is produced, lactose cannot be properly digested, resulting in abdominal discomfort within 30 minutes to two hours after consuming milk or milk-based foods.

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The degree of lactose intolerance varies from person to person. In most cases, the ability to digest lactose was present at birth but was lost, either suddenly or gradually, between the ages of three and 20. The condition is very common; indeed, it is estimated that over 70 percent of the world’s adult population cannot digest lactose, with the exception of people of northern European descent, of whom less than 20 percent are lactose-intolerant. Most African American, Asian and Native American adults produce little or no lactase. Lactose intolerance is not a health risk, and symptoms may be controlled by following simple dietary measures.

What Causes Lactose Intolerance?

  • Hereditary factors play a role in lactose intolerance.
  • Some chronic gastrointestinal disorders, such as irritable bowel syndrome, Crohn’s disease and ulcerative colitis, may cause lactose intolerance.
  • In infants, an intestinal infection such as gastroenteritis may cause temporary lactose intolerance.
  • An inadequate amount of the digestive enzyme lactase can cause lactose intolerance.

Symptoms of Lactose Intolerance

  • Abdominal pain, cramps and bloating
  • Excessive gas
  • Loose stools
  • Vomiting and nausea
  • Diarrhea
  • Flatulence
  • Audible bowel noises
  • Weight loss or slow growth in infants and young children
  • Malnutrition


There is no known way to prevent the development of lactose intolerance (although treatment can prevent symptoms).

Diagnosis of Lactose Intolerance

  • Lactose intolerance is suspected when stomach upset occurs shortly after consuming milk or other dairy products.
  • Ability to absorb lactose can be determined by administering lactose orally and measuring the resulting rise in blood glucose (lactose tolerance test), or by measuring the amount of hydrogen subsequently exhaled in the breath (hydrogen breath test).
  • To measure lactic acid in the stool for infants and small children, a stool acidity test may be performed.

How to Treat Lactose Intolerance

  • Eliminate or reduce the amount of dairy products in your diet, including milk, cream, cheese, butter and ice cream.
  • Experiment: You may be able to tolerate moderate amounts of milk if consumed with a meal. Lactose-reduced milk is available.
  • Add lactase drops to milk or swallow lactase tablets or caplets just prior to meals. The lactase in these over-the-counter supplements will break down most lactose in dairy products.
  • Try yogurt with live cultures. Yogurt contains less lactose than milk, and the bacteria predigest much of what remains. Look for live or active cultures listed on the label.
  • Substitute soy milk (a liquid made from soybeans) for cow’s milk. Soy milk may be fed to babies, poured on cereal, and used in baking.
  • Make sure to get enough calcium in your diet. Broccoli, calcium-fortified orange juice, amaranth (a grain) and legumes are good choices. Your doctor may advise calcium supplements as well.
  • Be aware that lactose is commonly found in many foods, including baked goods such as breads, cookies and cakes; pancake mixes; some powdered drinks such as cocoa and flavored coffees; processed meats such as frankfurters; and some canned and powdered soups.
  • Hard, aged cheeses, like cheddar and Parmesan, are very low in lactose.
  • Many medications contain lactose as an additive—check with your pharmacist.

When to Call a Doctor

See your doctor if self-treatment for lactose intolerance does not relieve abdominal discomfort.


Johns Hopkins Symptoms and Remedies: The Complete Home Medical Reference

Simeon Margolis, M.D., Ph.D., Medical Editor

Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 31 Aug 2011

Last Modified: 22 Jul 2015