The symptoms of lactose intolerance can start within hours of consuming lactose and last as long as someone includes lactose in their diet.

Lactose intolerance is an inability to digest and absorb lactose, which is the sugar in milk and dairy products.

Some people with lactose intolerance can manage small amounts of dairy products or replace them with lactose-free alternatives. Other people may use supplements to replace the enzyme lactase. However, some individuals may need to avoid all dairy products and plan their diet accordingly.

This article discusses lactose intolerance and how long its symptoms may last. It also explores how doctors treat the condition and how people can manage their calcium intake. Finally, it answers some common questions about the condition.

Nutrition resources

For more science-backed resources on nutrition, visit our dedicated hub.

Was this helpful?
Image of a plastic cup and straw spilling milk over a black backgroundShare on Pinterest
Catherine McQueen/Getty Images

Lactose intolerance is a condition that causes digestive symptoms after a person consumes food or drink containing lactose. Lactose is a sugar that occurs naturally in milk and milk products, such as cheese and yogurt.

A person with lactose intolerance lacks sufficient amounts of the enzyme lactase, which breaks down lactose. As a result, their body cannot break down the sugar and digest it. Doctors refer to this as lactose malabsorption.

The undigested lactose passes into the colon, where the bacteria ferment it, creating fluids and gas.


Symptoms of lactose intolerance can occur within hours of consuming foods or drinks containing lactose. They may be mild or severe and can include:

Causes of lactose intolerance

In some people, lactose intolerance has a genetic cause. Lactase nonpersistence, in which the body makes less lactase after infancy, is the most common cause of low lactase levels. Genetics plays a role in this condition.

Research indicates that lactase nonpersistence may have an evolutionary role for humans, as most mammals do not consume milk after weaning. Lactase persistence, when the body continues to produce lactase, occurs almost exclusively in populations with long histories of consuming dairy products.

People with lactase nonpersistence may experience symptoms in childhood or early adulthood when their lactase levels decline.

Congenital lactase deficiency is a rare genetic condition in which the small intestine makes little or no lactase from birth.

Lactose intolerance also has non-genetic causes. For example, damage to the small intestine may occur with Crohn’s disease or celiac disease, leading to a reduced production of lactase.

Some medications, surgery, or radiation therapy can injure the gut and cause lactose intolerance. When injury to the small intestine causes lactose intolerance, doctors refer to it as secondary lactose intolerance.

Some babies who have a premature birth may not be able to make lactase at first, but this may improve as they get older.

According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), how doctors manage symptoms depends on the cause of lactose intolerance.

If someone has lactase nonpersistence or congenital lactase deficiency, doctors cannot increase the amount of lactase that their intestines make. Therefore, a person needs to manage their diet, as their symptoms will persist while they continue to consume milk and dairy products.

Conversely, treating someone with an injury to their intestine may improve their symptoms, and they may be able to tolerate lactose afterward.

Some infants with lactose intolerance may grow out of it, and their symptoms may improve without treatment.

Dietary changes are the primary treatment for lactase nonpersistence or congenital lactase deficiency. Some people may only need to limit the lactose they eat or drink, while others must avoid it altogether. Doctors may also recommend taking lactase supplements.

Foods containing lactose

The following products contain lactose:

Many other foods may contain lactose if dairy products are among the ingredients. Examples include:

  • mashed potatoes with added butter or milk
  • pancakes and waffles
  • margarine
  • custard
  • some desserts

The NIDDK suggests that some people may be able to have 12 grams of lactose without symptoms or with milder symptoms. Additionally, they may be able to eat a little dairy at a time or eat products lower in lactose, such as yogurt and hard cheeses.

Lactase supplements

Lactase supplements are tablets or drops that contain the enzyme lactase to break down lactose. People take them before eating or drinking dairy or add drops to milk before they drink it.

However, a person should check with their doctor before using lactase products. These supplements may not be suitable for some people, such as young children or those who are pregnant.

Some research suggests that most humans are at risk of lactose intolerance because dietary guidelines often promote milk consumption.

Avoiding dairy products is a possible way to manage lactose intolerance, and many plant-based dairy alternatives are now available.

However, dairy products are a source of calcium for many people, and some individuals may be concerned that avoiding dairy may lead to osteoporosis.

A 2018 review suggested that scientists need to do more research to ascertain the benefits and risks of dairy products and determine whether plant-based alternatives are equally nutritious.

Manufacturers often fortify plant-based milks with nutrients for bone health, such as calcium and vitamin D. Additionally, someone may include the following plant-based sources of calcium in their diet:

Fish with bones and fortified cereals and juice may also contain calcium.

Below are the answers to some common questions about lactose intolerance.

Are there stages of lactose intolerance?

In the most common form of lactose intolerance, there is a gradual decline in lactase activity with increasing age. However, people with congenital lactase deficiency may have symptoms from birth, and those with an injury to the small intestine may have lactose intolerance following a health condition, surgery, or medication.

What is lactose-free milk?

Lactose-free milk still contains some essential vitamins and minerals, such as calcium, so it can be a healthy addition to the diet. People with lactose intolerance may drink lactose-free milk to help lower the amount of lactose in their diet.

Some stores also sell lactose-reduced milk, which may be suitable for people who can safely consume small amounts of lactose.

Which dairy products are lower in lactose?

Some types of cheese are naturally low in lactose, and some people may be able to tolerate eating them without symptoms. These include:

  • parmesan
  • cheddar
  • Swiss cheeses

Additionally, butter is naturally low in lactose, and yogurt contains less lactose than milk. People may also include lactose-free products or, in some cases, lactose-reduced dairy products in their diet.

The symptoms of lactose intolerance may last as long as someone includes lactose in their diet. Some people may tolerate lactose in smaller amounts, while others may not be able to tolerate any dairy products at all.

If someone has secondary lactose intolerance resulting from an injury to the intestines, their symptoms may improve following treatment for the injury. A person should seek advice from a doctor on managing their symptoms and then plan their diet accordingly.