Lactose Intolerance – Cause, Symptoms, Diagnosis, Treatment (2024)

Millions of Americans can’t digest a certain sugar in milk and milk products called lactose. If you’re one of them, you have lactose intolerance.

The condition isn’t harmful, but it can be uncomfortable and may be embarrassing. There’s no cure, but you can manage it by watching how much milk or milk products you drink or eat.

Being lactose intolerant is not the same as being allergic to milk. A food allergy is an immune system response.

What Is Lactose?

Lactose is the sugar that’s in milk.

Our bodies use an enzyme called lactase to break down that sugar so we can absorb it into our bodies. But people with lactose intolerance don’t have enough lactase. It’s produced in the small intestine.

Even with low levels of lactase, some people can digest milk products just fine. For people who are lactose intolerant, their low lactase levels give them symptoms after they eat dairy.

What is lactose malabsorption?

When you have lactose malabsorption, your small intestine can't absorb the lactose you've taken in. It passes through your digestive system unabsorbed. When it gets to your large intestine, it may cause symptoms – that's intolerance. If you have lactose intolerance, then by definition, you're not absorbing lactose and have symptoms. But you can have lactose malabsorption without lactose intolerance.

What percentage of people are lactose intolerant?

Lactose intolerance is common. The risk of it is linked to your ethnicity. Lactose intolerance affects about 85% of Black adults in the U.S. and about 15% of White adults. It's also more likely to affect you if you have Hispanic, Asian, Native American, or Jewish ancestry.

What Happens in My Body if I’m Lactose Intolerant?

When we drink milk or have a milk-based product, lactase in our small intestine breaks down the milk sugar. It then gets absorbed into the body through the small intestine.

But people who are lactose intolerant don’t have it so easy. In them, the lactose doesn’t get broken down. Instead, it goes on to the colon, where it mixes with normal bacteria and ferments. It can cause things like gas, bloating , and diarrhea.

The symptoms are no fun, but they’re not dangerous. Most people can manage their symptoms by changing their diet and limiting the amount of lactose they consume. Some people do better by cutting lactose out of their diet altogether.

Lactose Intolerance Causes

The main cause of lactose intolerance is that you produce too little lactase, the enzyme in your small intestine that breaks down lactose.

Your level of gut sensitivity also plays a role. It's not unusual to eat things your body can't fully digest. They pass through the small intestine into the colon, where they feed the bacteria living there. Those bacteria are different for each person. This is called your "gut biome." Every person's gut tolerance is different, because no two gut biomes are the same. That's why the level and the symptoms of lactose intolerance vary from person to person.

Can you develop lactose intolerance?

Most people become less tolerant of lactose as they get older, because our bodies produce less lactase as we age. Your gut biome changes, too. One study found that lactose malabsorption – which plays a key role in lactose intolerance – increases in people older than 65.

Lactose Intolerance Types

Lactose intolerance breaks down into four types.

Primary lactose intolerance

This is the most common type. It happens because your body gradually stops producing enough lactase for you to process dairy products.

Secondary lactose intolerance

This happens when an illness or injury causes your body to slow or stop making lactase. It could happen because of a condition like Crohn's disease, a bacterial infection of your intestines, or celiac disease. It might also start because you injured your small intestine or had surgery on it. Your lactose intolerance might improve – although slowly – once the other problem is dealt with.

Congenital lactose intolerance

It's rare, but you might be born not being able to produce enough lactase. This is caused by a gene you inherit from both parents.

Developmental lactose intolerance

Premature babies sometimes have lactose intolerance because their small intestines weren't fully developed at birth.

Lactose Intolerance Risk Factors

Most adults around the world can’t digest milk – 40% of humans stop producing enough lactase to digest milk between the ages of 2 and 5.

Risk factors for developing lactose intolerance include:

  • Age. You produce less lactase as you grow older.
  • Ethnicity. If your heritage is African, Asian, Hispanic, or Native American, your risk is higher.
  • Premature birth. Babies born early can have digestive systems that aren't fully developed.
  • Conditions that affect your small intestine. This includes things like Crohn's disease, celiac, and bacterial overgrowth.
  • Cancer treatment. Radiation and chemotherapy can affect your gut.

Lactose Intolerance Symptoms

Your symptoms might take hours to show up after you eat dairy products, because it takes time for the undigested lactose to move into your large intestine. They can include:

  • Bloating
  • Gas
  • Nausea and vomiting
  • Stomach cramps and pain
  • Diarrhea
  • Stomach noise – gurgling and rumbling

Lactose Intolerance Tests

Your body may be able to handle some lactose without symptoms. Experiment to find out the types and amounts of products with lactose you can eat and drink.

There are some steps you can take to test yourself:

  1. Go without milk or milk products for a couple of weeks.
  2. If your symptoms disappear, bring dairy products back into your diet a little at a time to take note of how you react.
  3. If your symptoms continue after cutting out the dairy – or if they return – see your doctor to find out what’s going on.

Your doctor can test for lactose intolerance:

  • Breath test. This will show if you have high levels of hydrogen when you exhale. If you do, you might be lactose intolerant. That’s because hydrogen is given off when lactose is broken down in the colon. The hydrogen gets taken by the blood up to your lungs, and then you exhale it.
  • Blood test. This can show how your body reacts after you drink something with a lot of lactose. Your doctor might do this test if the results of the breath test aren't clear.
  • Stool acidity test. This is the test used for children and infants. The health care provider will take a sample of your child's poop after they've eaten something with lactose. By analyzing the lactic acid and other substances in the sample, they can tell whether your child is digesting lactose.
  • Genetic test. Using a sample of your blood or spit, a lab checks to see if your genes could be behind your lactose intolerance.
  • Surgical biopsy. This is done in a hospital under anesthesia. The surgeon makes a cut in your stomach and takes a sample of your small intestine tissue. A lab then checks the sample for signs of lactose intolerance.

Lactose Intolerance Treatment

You may be able to eat or drink small amounts of dairy. Some people do better if they have it with a meal. And some dairy products, like hard cheese or yogurt, may be easier to digest.

Also, there are lots of lactose-free dairy products at the supermarket. Or you can take commonly found over-the-counter supplements (like Lactaid) to break down the milk sugars if you still want the real thing.

Talk to your doctor about a liquid lactase replacement. These are over-the-counter drops that you add to milk.

Eating foods that contain probiotics might help with your lactose intolerance. Researchers are looking into whether lactic acid bacteria in probiotics might stop your body from turning undigested lactose into gas. Studies have shown that yogurt with lactic acid probiotics can help with lactose intolerance, but more research is needed.

If you give up milk completely, you can still get plenty of calcium, vitamin D , and other nutrients in a healthy diet.

Instead of milk, you can substitute these foods:

  • Almonds
  • Dried beans
  • Tofu
  • Collards
  • Kale
  • Calcium-fortified orange juice and soy milk
  • Fatty fish, like salmon, tuna, and mackerel
  • Egg yolks
  • Beef liver

How to stop lactose intolerance pain

The symptoms of lactose intolerance are uncomfortable; your best bet to manage that pain is to watch your diet and limit how much dairy you eat and drink.

What Foods Contain Lactose?

Always read labels. Many foods have lactose, including snack foods, bakery products, candy, dry mixes, dried vegetables, and infant formulas.

Many medicines also have lactose, which is used as a filler, especially in white tablets. Many birth control pills and medications used to treat gas and stomach acid contain lactose. Your doctor or pharmacist can let you know if any prescription medications you take contain lactose.

Some high-lactose foods to watch out for:

  • Milk and heavy cream
  • Condensed and evaporated milk
  • Ice cream
  • Cottage cheese
  • Ricotta cheese
  • Sour cream
  • Cheese spreads

Lactose-free alternatives

Look for foods you can substitute for those with lactose. They include:

  • Soy milk. It’s high in protein, potassium, and antioxidants.
  • Rice beverages
  • Lactose-free milk. It’s high in calcium and protein and contains many other vitamins, such as A, B, and K, zinc, potassium, and magnesium.
  • Almond milk
  • Coconut milk

If you have symptoms of lactose intolerance, see your doctor. And if you’re diagnosed with it, talk with them about how to be sure you’re eating right.


Lactose intolerance is a common condition. When you have it, your body doesn't break down lactose, the sugar that's in milk and dairy products. That can lead to symptoms such as gas, bloating, nausea, and diarrhea. Steps you can take to manage lactose intolerance include learning what foods contain lactose, limiting the amount of dairy in your diet, and taking a supplement to help you digest lactose.

Lactose Intolerance FAQs

Why am I suddenly lactose intolerant?

The most common form of lactose intolerance happens as people age. As you get older, your body produces less lactase, the enzyme you need to break down the sugar in milk and dairy products. You also can develop lactose intolerance because you have a digestive condition like Crohn's disease, you've had surgery on your intestines, or you're having treatment for cancer.

What happens if lactose intolerance goes untreated?

The symptoms of lactose intolerance are unpleasant, but they're not dangerous. There's no need to keep experiencing them, though. You can adjust your diet and take other steps to deal with lactose intolerance. The main long-term concern is that if you eliminate dairy from your diet, you might not get enough calcium or vitamin D. But there are ways to get those nutrients without eating dairy.

Lactose Intolerance – Cause, Symptoms, Diagnosis, Treatment (2024)
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