Key Points about Lactose Intolerance

  • People with lactose intolerance cannot fully digest lactose, the sugar in milk and milk products.
  • A deficiency of lactase, an enzyme produced in the small intestine, is usually responsible for lactose intolerance.
  • Symptoms of lactose intolerance include diarrhea, nausea, abdominal cramps, bloating, and gas following the consumption of dairy products.
  • There is no cure for lactose intolerance, although avoiding lactose can prevent symptoms from occurring.
  • Over-the-counter medications such as Lactaid can reduce symptoms of lactose intolerance in some people.
Common related conditions
Bloody Stool Constipation Diarrhea Celiac Disease Heartburn Irritable Bowel Syndrome


Lactose intolerance is a condition in which the body cannot fully digest lactose, the sugar in milk and milk products. People with lactose intolerance may experience diarrhea, nausea, abdominal cramps, bloating, and gas following the consumption of dairy products.

While there is no cure for lactose intolerance, avoiding foods that contain lactose can prevent symptoms that cause discomfort. Your doctor can administer tests to diagnose lactose intolerance if you think you may be affected.

Lactose intolerance causes

Lactose intolerance is usually a result of a deficiency of lactase, an enzyme produced in the small intestine.

In people with lactose intolerance, instead of broken-down lactose being absorbed into the bloodstream, undigested lactose travels to the colon where it interacts with normal bacteria to produce the symptoms of lactose intolerance.

There are three types of lactose intolerance:

  • Primary lactose intolerance — The most common form of lactose intolerance, primary lactose intolerance occurs when a person’s lactase production drops off sharply before or during adulthood. In people without lactose intolerance, the small intestine reduces the amount of lactase it produces as a person gets older, but still produces enough of the enzyme to digest a moderate amount of dairy.
  • Secondary lactose intolerance  This form of intolerance occurs when lactase production decreases following an illness or procedure in your small intestine. Lactose intolerance that develops after celiac disease, Chron’s disease, or bacterial overgrowth are examples of secondary lactose intolerance.
  • Congenital (developmental) lactose intolerance — This is a rare, genetically inherited, autosomal recessive disorder that leaves infants without any lactase production. 

Lactose intolerance risk factors

Risk factors for developing lactose intolerance include:

  • Older age — Adults develop lactose intolerance more often than children. 
  • Ethnicity — People of African, Asian, Hispanic, and American Indian descent are more likely to be lactose intolerant. 
  • Premature birth — Lactase-producing cells develop late in the third trimester. As a result, prematurely born infants may have lower levels of lactase, leading some to experience lactose intolerance.
  • Small intestine diseases — Bacterial overgrowth, celiac disease and Chron’s disease can lead to lactose intolerance.

Lactose intolerance symptoms

Symptoms of lactose intolerance, which tend to begin within 30 minutes of consuming lactose, include:

  • Diarrhea
  • Nausea or vomiting
  • Abdominal cramps
  • Bloating
  • Gas

Lactose intolerance diagnosis

Doctors may give the following tests to diagnose lactose intolerance:

  • Lactose intolerance test
  • Hydrogen breath test
  • Stool acidity test

Lactose intolerance treatment

There is no treatment, currently, to increase your body’s natural production of lactase.

To avoid the physical discomforts of lactose intolerance:

  • Avoid large amounts of milk and dairy products
  • Choose reduced-lactose products when available
  • Try over-the-counter tablets containing the lactase enzyme, such as Lactaid

Most people with lactose intolerance are still able to keep some dairy products in their diet.

When to seek care

Consult your doctor if you frequently experience diarrhea, nausea, abdominal cramps, bloating, or gas after eating dairy foods.

Next Steps

There are other ways to get enough calcium when avoiding milk and dairy products. Non-dairy foods that contain calcium include:

  • Broccoli
  • Oranges
  • Pinto beans
  • Spinach
  • Soy and rice milk
  • Calcium-fortified products such as some breads and juices

A doctor or dietician can help you create a comprehensive, balanced diet plan that excludes dairy.

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