Fast facts: developing lactose intolerance later in life.

Our content is not intended nor recommended as a substitute for medical advice by your doctor. Use for informational purposes only.

You can develop lactose intolerance later in life at any age. The most common pattern of lactose intolerance is primary lactase deficiency. In the primary type, you will develop symptoms of lactose intolerance later during adolescence or early adulthood.

Other types of lactose intolerance and the typical age of presentation are (reference):

  • Adolescence and early adulthood: the most common age of the development of lactose intolerance. It is due to primary lactase deficiency.
  • At any age (even later in life): when a disease causes destruction to the brush border of the small intestine.
  • Soon after birth: in the congenital and developmental types of lactase deficiency.

1 . Primary lactase deficiency (The most common form of lactose intolerance).

Lactose intolerance results from a deficiency in the lactase enzyme. The lactase enzymes help the breakdown, digestion, and absorption of lactose sugar in milk.

The most common cause of a hereditary deficiency of the enzyme. However, the symptoms don’t develop at birth.

The lactase enzyme gradually and slowly declines in activity with age. At first, the decline is so minimal and the patient will remain asymptomatic for several years.

At some point, when the deficiency becomes significant, symptoms of lactose intolerance develop.

Primary lactose intolerance symptoms often develop later during adolescence or early adulthood.

The symptoms often start shortly after consuming milk or other dairy products. common symptoms include:

  • Diarrhea.
  • Abdominal pain.
  • Bloating.
  • Distension and gas.
  • Nausea after eating or drinking milk.
  • A sense of fullness.
  • Less commonly, headaches, muscle pain, joint pain, and loss of concentration.

2. Secondary lactase deficiency.

The lactase enzymes are located at the lining of the small intestine (brush border of the small intestine). Any destruction or disease affecting the brush border of the small intestine can lead to lactase enzyme deficiency.

The secondary type of lactose intolerance develops at any age even later in life. The disease is often triggered by:

  • An attack of severe gastroenteritis.
  • Celiac disease.
  • Crohn’s disease (a type of inflammatory bowel disease).
  • Ulcerative colitits.
  • Chemotherapy.
  • Antibiotic use.

The secondary type of lactose intolerance is less common than primary lactase deficiency. It can develop at any age and it is often linked to other diseases affecting the small intestine.

3. Congenital lactase defeciency.

This is a rare form of lactose intolerance. It results from a genetic defect (autosomal recessive). Congenital lactase deficiency is more severe and presents early in life.

Often, It develops very early as soon as the newborn ingests milk.

4. Developmental lactase deficiency.

Developmental lactase deficiency occurs as a result of incomplete maturation of the small intestine (the site of lactase enzyme).

Developmental lactase deficiency affects preterm babies born between 28 to 73 weeks of pregnancy. The symptoms of lactose intolerance develop soon after birth. However, it improves with age (due to the maturation of the small intestine).


  • Lactose intolerance is very common, About 65% of people worldwide are lactose intolerant
  • The most common type of lactose intolerance is the primary type. The deficiency of the lactase enzyme starts to decline during infancy, but the symptoms of lactose intolerance will develop later during adolescence or adult life.
  • Secondary lactose intolerance occurs as a result of severe infections (gastroenteritis) or diseases destructing the small intestinal lining. It can develop at any stage of life including adulthood.
  • Other less common types are congenital lactase deficiency which develops soon after birth and developmental lactase deficiency which affects premature infants due to immature intestines.