Lactose intolerance is a sign of inability to fully digest the sugar (lactose) that is present in milk. Lactose intolerance, also known as lactose malabsorption, causes diarrhea, gas and bloating after consuming dairy products.

Deficiency of lactase (enzyme produced in the small intestine) is usually the cause of lactose intolerance. Lactase deficiency leads to symptoms after consuming dairy products. The condition is mainly harmless but the symptoms can cause discomfort.

In most cases, the condition can be managed effectively without giving up all dairy products.



Symptoms of lactose intolerance include:


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



Lactose intolerance is the result of the insufficient production of the lactase enzyme by the small intestine. Lactase is used to digest milk sugar (lactose) by turning it into simple sugars (glucose and galactose).

Lactase deficiency causes the lactose from food to move into the colon where the undigested lactose interacts with normal bacteria causing the symptoms of lactose intolerance.

Lactose intolerance can be classified into three categories. Different factors cause lactase deficiency in each category.


Primary lactose intolerance


Primary lactose intolerance is the most common type. People who develop primary lactose intolerance produce sufficient lactase at the beginning of their life. However, lactase production decreases with increasing age, which may lead to primary lactose intolerance where lactase production plummets. As a result dairy products become more difficult to digest in adulthood.

Primary lactose intolerance is genetically predetermined and most cases occur in people of African, Asian or Hispanic descent.


Secondary lactose intolerance


Secondary lactose intolerance is the result of a decreased production of lactase after an illness, surgery or an injury involving the small intestine. The main conditions associated with this type of lactose intolerance are bacterial overgrowth, celiac disease and Crohn’s disease. Treatment of the underlying condition may improve the symptoms of lactose intolerance and possibly restore lactase levels.


Congenital or developmental lactose intolerance


This type of lactose intolerance is inherited from the parents through an autosomal recessive pattern, which causes complete absence of lactase activity.


Risk factors


Risk factors for lactose intolerance include:


  • Increasing age: Lactose intolerance generally occurs in adulthood.
  • Ethnicity: Most common cases of lactose intolerance are recorded in people of African, Asian, Hispanic or American Indian descent.
  • Premature birth: Premature infants have an increased risk of lactose intolerance due to the reduced levels of lactase. Lower levels of lactase are the result of underdeveloped lactase-producing cells in the small intestine.
  • Diseases that affect the small intestine: Bacterial overgrowth, celiac disease and Crohn’s disease can lead to lactose intolerance.
  • Cancer treatments: Radiation therapy for abdominal cancer or intestinal complications from chemotherapy can cause lactose intolerance.