An Overview of Lactose Intolerance

It's different than a dairy allergy and you may not need to avoid milk entirely

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Lactose is the natural sugar in milk and dairy foods. Your small intestine produces an enzyme called lactase to break this sugar down for digestion.

When you don't have enough of this enzyme to digest lactose, you can experience abdominal discomfort and digestive issues after eating dairy products like milk, ice cream, yogurt, and cheese. This is known as lactose intolerance.

Lactose intolerance is not the same as a lactose allergy. An intolerance means you can still consume dairy if you take some steps to help your body with lactose digestion. That said, some choose to avoid dairy altogether to take the possibility of symptoms off the table.

This article discusses the causes and symptoms of lactose intolerance. It also covers how lactose intolerance is diagnosed and different options for managing the condition.


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This video has been medically reviewed by Chris Vincent, MD.

Lactose Intolerance Symptoms

Lactose intolerance symptoms in adults, which occur only after lactose is consumed, may include:

  • Abdominal cramping
  • Gas
  • Bloating
  • Nausea
  • Diarrhea
  • Abdominal pain

Most of the time, these symptoms occur between half an hour to a couple hours after eating dairy products. Typically, the severity of symptoms corresponds with how much of the offending food and/or drink was consumed.

While classic lactose intolerance symptoms, these are fairly general symptoms that may occur because of several other conditions as well.

In Children

Though it's most common in adults, lactose intolerance can also affect children as early as age two. If you have a child with lactose intolerance, it can be a problem throughout their life or they may outgrow it.

The symptoms of lactose intolerance in children are the same those in adults. You may also notice that your child is cranky or has mood swings after they consume dairy products due to the discomfort they feel.

Keep in mind that breastmilk and infant formula made with cow's milk both contain lactose. If your infant consistently becomes cranky and has symptoms of lactose intolerance after being fed one of these, see their pediatrician.


Abdominal pain, gas, and cramping are common symptoms of lactose intolerance, but this can vary from person to person. Symptoms also overlap with those of other conditions, so it's important to see your doctor and get a formal diagnosis.

Lactose Intolerance or Dairy Allergy?

A dairy allergy is not the same as lactose intolerance. With dairy allergy, the immune system works to fight the proteins in milk, even though they are not inherently harmful.

Symptoms of dairy allergy are different from lactose intolerance, too. If you or your child has an allergic reaction to a dairy product, you should call 911 or get to a hospital right away.

Symptoms of dairy allergy include:

  • Swelling of the face, lips, tongue, or throat
  • Itching or tingling of the lips
  • Hives
  • Wheezing or coughing
  • Shortness of breath


If you have severe lactose intolerance, some complications can occur. Frequent vomiting or diarrhea can cause dehydration, weight loss, or imbalances in electrolytes—particles that have several roles in the body, including helping your muscles contract and your nerves send signals.

If you have a gastrointestinal (GI) infection, the effects of your lactose intolerance can be more noticeable until the infection resolves. And if you have a GI condition such as inflammatory bowel disease or irritable bowel syndrome, it can make your lactose intolerance worse.

Some people who have lactose intolerance avoid all dairy products. As a result, they can become deficient in important nutrients such as calcium, vitamin D, and protein.

These deficiencies can cause a number of health effects, such as bone fragility.


A lactose intolerance is not a dairy allergy. Still, it can have negative effects such as dehydration and weight loss due to vomiting or diarrhea. Passing on dairy products to avoid symptoms can also lead to nutritional deficiencies.


Your body stops making lactase by age 5. From there, levels of this enzyme decrease. Without enough lactase to to break down lactose into glucose and galactose—sugars that your body can absorb and use—the lactose sits in your digestive system.

For some, a naturally occurring bacteria called lactic acid bacteria can take over for the missing lactase. But even with that present, that may not be enough to digest lactose.

This causes fluid to flow into your colon, where bacteria feed on it and cause symptoms of lactose intolerance, such as diarrhea and stomach cramps. It is only after this that it eventually leaves the body in feces.

Almost 70% of the world's population has some form of lactose intolerance. Approximately 30 million American adults have some degree of lactose intolerance by the time they are 20 years old.

The decrease in the lactase enzyme, called lactose non-persistence, is the most common cause of lactose intolerance.

Genetics is the least common cause. Parents may pass an intolerance onto a child, in which case the condition may begin from birth. Infants with this condition may be unable to digest breast milk and require a lactose-free formula.

Others may experience lactose intolerance due to a digestive disorder. Conditions such as Crohn's disease or celiac disease can damage the intestinal cells that produce lactase.

In some cases, the intolerance can come about suddenly.

Sudden Lactose Intolerance

For many people, the condition seems to come on suddenly, even if they never had a problem with eating or drinking products with lactose before.

Lactose intolerance may be triggered by an illness, injury, or surgery that affects your small intestine. Conditions such as celiac disease and Crohn's disease fall into this group, as do stomach infection (gastroenteritis), inflammatory bowel disease, or a bacterial overgrowth in your small intestine.


Without enough lactase, your body cannot break down the sugar in dairy products. This most often happens because of declines in lactase as you age, but can also be inherited or due to a condition that affects your small intestine, such as Crohn's disease.

Foods That Trigger Lactose Intolerance

Since lactose is the natural sugar found in milk, cheese, and other dairy products, a person with lactose intolerance will experience symptoms any time they consume one of those products.

Foods that commonly trigger lactose intolerance include:

  • Milk
  • Ice cream
  • Cheese
  • Yogurt
  • Smoothies
  • White, milk-based sauce
  • Food cooked with cheese, such as pizza or macaroni and cheese
  • Cream dessert filling
  • Custard and pudding
  • Whipping creams
  • Milk-based creamer, half and half

Some people may experience lactose intolerance from consuming certain foods, but not others.


If you experience symptoms of lactose intolerance, it is best to speak with your healthcare provider to get a formal diagnosis and advice that is tailored specifically to your health and medical needs.

Many people determine that they or their child has lactose intolerance simply because they experience symptoms after consuming dairy. While your assumption may prove to be true, keep in mind that other medical problems can produce similar symptoms. Examples include infection, inflammatory bowel disease, malabsorption, and food allergy.

Elimination Diet

An elimination diet may be helpful in diagnosing lactose intolerance. With this, you eliminate all dairy products to see if the symptoms resolve.

It is important to only eliminate dairy when doing this. If you don't, you won't be as certain about what foods are triggering your symptoms.

Diagnostic Tests

Lactose intolerance can be diagnosed by a variety of tests. These include a lactose tolerance test, a breath test, or a stool sample test.

  • Lactose tolerance test: This blood test measures your blood glucose (blood sugar) after drinking lactose. If you can't properly break down and absorb lactose, your blood glucose level will not rise as much as expected after consuming the drink.
  • Hydrogen breath test: This test measures the hydrogen in your breath after you drink a lactose-containing beverage. High amounts of hydrogen suggest that you may not be able to break down the lactose.
  • Stool test: A stool sample is analyzed to measure undigested lactose in the stool. This is often used for infants and young children.


Treatment for lactose intolerance consists of either avoiding some or all lactose-containing foods or supplementing your body's supply of lactase enzyme so that you can better digest dairy if you do consume it.

When an underlying condition causes lactose intolerance in a child, treating the condition will typically resolve the lactose intolerance symptoms within three to four weeks.

Adults are less likely to "cure" their intolerance. Lactase levels can be restored in adults, but the process can take some time and is not always possible. Treatment, therefore, is really focused on management.

Diet Changes

You may determine that you feel your best when you cut out all dairy. However, this may not be necessary for everyone.

You may notice that you are able to tolerate cheese but not ice cream, or yogurt but not milk, for example. It is perfectly fine to consume the foods and drinks that don't cause you any problems, while avoiding the products that do.

It's worth mentioning your diet changes to your healthcare provider so they can lookout for possible nutrient deficiencies that may result from eliminating foods from your diet.

If calcium is a concern, know that you can also get this important nutrient from non-dairy sources, including fortified cereals and orange juice, kale, collard greens, garbanzo beans, and cooked broccoli.

Lactose-free milk and lactose-free ice cream are available in most grocery stores. Like regular milk, these also contain calcium and vitamin D. Most people who have lactose intolerance do not experience symptoms when consuming these lactose-free dairy options.


Over-the-counter lactase enzyme supplements can be taken before eating dairy products, but they are only effective if you get the timing right. Be sure to follow the package directions when taking these so that you have the beneficial effects when you need them.

Probiotics—helpful bacteria that naturally live in the digestive tract—may help ease symptoms in some people with lactose intolerance as well.

If your healthcare provider suggests probiotics for you, you use probiotic capsules, which are found in the refrigerated section of a health food store. You can also get probiotics by consuming options such as pickles, kimchi, tempeh, sauerkraut, and kombucha.


If you think you could be lactose intolerant, visit your doctor to make sure your symptoms aren't caused by something else. Your doctor will perform tests that check how well your body breaks lactase down. From there, you may be advised to avoid lactose-containing foods and drinks, or to try taking probiotics or lactase supplements.


When you are an infant, your body creates the enzyme lactase, which breaks down lactose—the sugar found naturally in milk and other dairy products. Your body stops making lactase after you are 2 to 5 years old. That's why lactose intolerance becomes more common as you get older.

Lactose intolerance symptoms like diarrhea, gas, and bloating can begin a half hour or more after consuming a food or drink that contains lactose.

If you are lactose intolerant, you may be able to avoid these symptoms by not consuming lactose or by taking OTC lactase supplements or probiotics.

Frequently Asked Questions

  • How common is lactose intolerance?

    Worldwide, upwards of 70% of adults are lactose intolerant. It's uncommon for children under 5 to have the condition.

  • What happens in your body when you're lactose intolerant?

    Your small intestine is unable to digest a sugar called lactose due to a lack of an enzyme called lactase. That lactose moves along your digestive tract to the colon. Gas that causes flatulence and bloating, diarrhea, and other symptoms then occur.

  • Is it possible to suddenly become lactose intolerant?

    Yes. Some people, especially those of African, Asian, or Hispanic descent, produce increasingly less lactase with age and may suddenly no longer be able to eat dairy products they once enjoyed. A sudden intolerance can also occur if you have a condition that damages the lining of the small intestine, such as celiac disease.

  • What are the best alternative sources of calcium for people with lactose intolerance?

    Among the richest non-dairy sources of calcium are:

    • Calcium-fortified foods and beverages, such as orange juice, soy milk, cereals, and bread
    • Canned fish with bones, such as sardines and salmon
    • Leafy green vegetables, including broccoli, collards, mustard greens, kale, and bok choy
    • Almonds and Brazil nuts
    • Sunflower seeds
    • Tahini
    • Blackstrap molasses
    • Dried figs

  • Should I take calcium supplements if I'm lactose intolerant?

    If you're unable to eat any amount of dairy foods and can't meet the recommended daily allowance for calcium with alternative sources, a supplement likely is advisable. Seek advice on what supplement to take and in what dose from your healthcare provider. A typical dose is 1,200 to 1,500 milligrams per day.

  • Why does milk make my stomach hurt?

    Lactose intolerance is a common cause of upset stomach after drinking milk. Your stomach might also hurt if you have a cow's milk allergy or irritable bowel disease, though there are other, more serious possibilities. See your doctor for a proper diagnosis.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Victoria Groce
Victoria Groce is a medical writer living with celiac disease who specializes in writing about dietary management of food allergies.