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Lactose intolerance

Medically reviewed by Drugs.com. Last updated on Mar 5, 2022.

Overview

People with lactose intolerance are unable to fully digest the sugar (lactose) in milk. As a result, they have diarrhea, gas and bloating after eating or drinking dairy products. The condition, which is also called lactose malabsorption, is usually harmless, but its symptoms can be uncomfortable.

Too little of an enzyme produced in your small intestine (lactase) is usually responsible for lactose intolerance. You can have low levels of lactase and still be able to digest milk products. But if your levels are too low you become lactose intolerant, leading to symptoms after you eat or drink dairy.

Most people with lactose intolerance can manage the condition without having to give up all dairy foods.

Colon and small intestine

The small intestine and colon are parts of your digestive tract, which processes the foods you eat. The intestines take nutrients from the foods. What isn't absorbed by the intestines continues along the digestive tract and is passed as stool during a bowel movement.

Symptoms

The signs and symptoms of lactose intolerance usually begin from 30 minutes to two hours after eating or drinking foods that contain lactose. Common signs and symptoms include:

When to see a doctor

Make an appointment with your doctor if you frequently have symptoms of lactose intolerance after eating dairy foods, particularly if you're worried about getting enough calcium.

Causes

Lactose intolerance occurs when your small intestine doesn't produce enough of an enzyme (lactase) to digest milk sugar (lactose).

Normally, lactase turns milk sugar into two simple sugars — glucose and galactose — which are absorbed into the bloodstream through the intestinal lining.

If you're lactase deficient, lactose in your food moves into the colon instead of being processed and absorbed. In the colon, normal bacteria interact with undigested lactose, causing the signs and symptoms of lactose intolerance.

There are three types of lactose intolerance. Different factors cause the lactase deficiency underlying each type.

Primary lactose intolerance

People who develop primary lactose intolerance — the most common type — start life producing enough lactase. Infants, who get all their nutrition from milk, need lactase.

As children replace milk with other foods, the amount of lactase they produce normally drops, but usually remains high enough to digest the amount of dairy in a typical adult diet. In primary lactose intolerance, lactase production falls off sharply by adulthood, making milk products difficult to digest.

Secondary lactose intolerance

This form of lactose intolerance occurs when your small intestine decreases lactase production after an illness, injury or surgery involving your small intestine. Diseases associated with secondary lactose intolerance include intestinal infection, celiac disease, bacterial overgrowth and Crohn's disease.

Treatment of the underlying disorder might restore lactase levels and improve signs and symptoms, though it can take time.

Congenital or developmental lactose intolerance

It's possible, but rare, for babies to be born with lactose intolerance caused by a lack of lactase. This disorder is passed from generation to generation in a pattern of inheritance called autosomal recessive, meaning that both the mother and the father must pass on the same gene variant for a child to be affected. Premature infants can also have lactose intolerance because of an insufficient lactase level.

Risk factors

Factors that can make you or your child more prone to lactose intolerance include:

Diagnosis

Your doctor might suspect lactose intolerance based on your symptoms and your response to reducing the amount of dairy foods in your diet. Your doctor can confirm the diagnosis by conducting one or more of the following tests:

Treatment

In people with lactose intolerance caused by an underlying condition, treating the condition might restore the body's ability to digest lactose, although that process can take months. For other causes, you might avoid the discomfort of lactose intolerance by following a low-lactose diet.

To lower the amount of lactose in your diet:

Self care

With some trial and error, you might be able to predict your body's response to foods containing lactose and figure out how much you can eat or drink without discomfort. Few people have such severe lactose intolerance that they have to cut out all milk products and be wary of nondairy foods or medications that contain lactose.

Maintain good nutrition

Reducing the dairy products doesn't mean you can't get enough calcium. Calcium is found in many other foods, such as:

Also make sure you get enough vitamin D, which is typically supplied in fortified milk. Eggs, liver and yogurt also contain vitamin D, and your body makes vitamin D when you spend time in the sun.

Even without restricting dairy foods, though, many adults don't get enough vitamin D. Talk to your doctor about taking vitamin D and calcium supplements to be sure.

Limit dairy products

Most people with lactose intolerance can enjoy some milk products without symptoms. You might tolerate low-fat milk products, such as skim milk, better than whole-milk products. It also might be possible to increase your tolerance to dairy products by gradually introducing them into your diet.

Ways to change your diet to minimize symptoms of lactose intolerance include:

Alternative medicine

Probiotics

Probiotics are living organisms present in your intestines that help maintain a healthy digestive system. Probiotics are also available as active or "live" cultures in some yogurts and as supplements in capsule form.

They are sometimes used for gastrointestinal conditions, such as diarrhea and irritable bowel syndrome. They might also help your body digest lactose. Probiotics are generally considered safe and might be worth a try if other methods don't help.

Preparing for your appointment

Start by seeing your family doctor if you have signs or symptoms that suggest you may have lactose intolerance. Here's some information to help you get ready.

What you can do

When you make the appointment, be sure to ask if there's anything you need to do in advance, such as restrict your diet.

Make a list of:

Questions for your doctor about lactose intolerance might include:

What you can do in the meantime

Keep track of your daily servings of dairy foods, including milk, ice cream, yogurt and cottage cheese, and when you have them and what you eat with them. Also let your doctor know which dairy foods, in what amounts, give you symptoms. This information can help your doctor make a diagnosis.

If you think you may have lactose intolerance, try cutting dairy products from your diet for a few days to see if your symptoms ease. Let your doctor know if your symptoms got better on the days you didn't have dairy products.

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