If you have lactose intolerance, it means you’re unable to fully digest the lactose in milk. For people with lactose intolerance, drinking milk or eating dairy products can result in:

Lactose intolerance — also referred to as lactose malabsorption — is usually caused by having too little of an enzyme produced in your small intestine called lactase.

Lactose intolerance can be developed at any age. There are four main types:

  • primary
  • congenital
  • developmental
  • secondary

Primary and congenital lactose intolerance are both inherited.

Primary lactose intolerance is the most common. Your lactase production starts to decrease as you age and you become less dependent on dairy, usually after the age of 2.

You may not notice symptoms, however, until you’re an adult. It may seem like lactose intolerance has developed, but primary lactose intolerance is hereditary.

Congenital lactose intolerance is a rare condition found in newborn babies. It’s inherited instead of developed. Both parents need the gene mutation to pass it on.

Developmental lactose intolerance is typically temporary. It’s found in some babies born prematurely before their small intestine was fully developed.

Secondary lactose intolerance isn’t hereditary, but is developed when you have a problem in your small intestine. It can occur at any age.

Secondary lactose intolerance is caused by a problem in your small intestine. If this problem creates a shortage of lactase, then you may develop lactose intolerance.

Possible causes of secondary lactose intolerance include:

As you get older, your body naturally produces less lactase. This can cause you to develop secondary lactase intolerance without a triggering condition.

You can develop lactose intolerance at any age. It could be triggered by a condition, such as Crohn’s disease or gastroenteritis. This can result in your small intestine producing an inadequate supply of lactase.

Also, as you age, your body naturally starts to product less lactase and that could result in the development of lactose intolerance.