What Are the Most Common Symptoms of Lactose Intolerance?

Have you ever had a glass of milk or a bowl of cereal and found yourself regretting the decision a few hours later when the cramping and bloating kicks in? You might be surprised to learn that many people have the same problem. 

Lactose intolerance is very common. But there are ways to relieve symptoms so you don’t have to give up dairy completely. Let’s take a look at the causes and treatment options for lactose intolerance. 

What is lactose intolerance?

Lactose is the sugar in milk and milk products. All types of milk, including human milk, contain lactose. Your body makes an enzyme called lactase to break down lactose so it can be absorbed by the intestines. 

Some people make less lactase, so they have trouble digesting lactose. When it is not digested, lactose will move from the small intestines to the large intestines (colon) without being absorbed. In the colon, lactose gets broken down by gut bacteria, which creates gas. This gas is what creates lactose intolerance symptoms.

What are the symptoms of lactose intolerance?

The symptoms of lactose intolerance include:

• Stomach pain and cramping

• Bloating 

• Gas (flatulence)

• Nausea and vomiting

• Diarrhea (more common in children)

These symptoms aren’t dangerous to health. But they are very uncomfortable and distressing. 

Symptoms from lactose intolerance begin a few hours after someone eats milk or milk products. But symptoms can be unpredictable in terms of timing and severity. The randomness of the symptoms can affect your ability to plan your daily activities because you don’t know when or where you’ll have symptoms or how bad they’ll be. 

Quiz: Am I lactose intolerant?

Why do people get lactose intolerance?

People get lactose intolerance because they either have less lactase in their gut, or the lactase they do have in their gut doesn’t work well.

There are several reasons lactose intolerance can happen.

Genetics

Most people are born with plenty of lactase. After all, as babies, we depend on some kind of milk for nutrition. As we get older, we depend less on milk for nutrition, so our bodies start making less lactase. 

Except in rare cases, most people make plenty of lactase until they are 4 to 5 years old. As they get older, people make less and less lactase. In these cases, if people continue to consume milk and milk products throughout their lives, it’s likely they will experience symptoms of lactose intolerance. 

Studies show that some people keep making lactase at high levels throughout their lives. These people tend to belong to racial groups who have historically relied on milk as a lifelong primary source of nutrition.

Injury to the small intestine

Lactase is made by special cells in the small intestine. If these cells get hurt, they can’t make lactase. This inability is another cause of lactose intolerance. 

Surgery and infection are the most common reasons for lactase production to drop. Even a mild infection like gastroenteritis — also known as the stomach flu — can wipe out lactase in the small intestine. Many people who get lactose intolerance symptoms all of a sudden are actually recovering from this type of injury. Eventually, these cells grow back and start making lactase again, and symptoms gradually go away. 

Medical conditions

People with inflammation in their small intestines, like Crohn’s disease, also don’t make a lot of lactase. 

Babies who are born prematurely don’t make much lactase either, because their small intestine is not fully developed yet. 

Diagnosing lactose intolerance

If you think you could have lactose intolerance, and it’s getting in the way of everyday life, then it’s a good idea to see your healthcare provider. The same is true if you think your child could have lactose intolerance. It is very rare for children younger than preschool age to have lactose intolerance, so if you have a young child with symptoms of lactose intolerance, you’ll want to see their healthcare provider more urgently. 

The first step for you to determine if you have an intolerance usually is to stop your lactose intake for 7 to 10 days. If symptoms resolve, that’s a good sign your diagnosis is right. But sometimes more tests and more time are needed.  

If your healthcare provider needs more information, they might also do a:

• Hydrogen breath test: You will blow into a machine after drinking a liquid that contains lactose. A high amount of hydrogen in your breath means that you aren’t absorbing lactose.

• Lactose tolerance test: You will drink a liquid containing lactose and then have your blood sugar checked 1 and 2 hours later. If your blood sugar doesn’t go up, that means you aren’t absorbing lactose.

How do you treat lactose intolerance?

There’s no way to get your body to make more lactase. But don’t despair: Most people don’t have to give up lactose completely. There are many things people can do to improve symptoms of lactose intolerance: 

• Eat small amounts of lactose at a time. Most people with lactose intolerance still make some lactase. By taking in less lactose at once, lactase won’t get overwhelmed and will be able to break down the lactose. Over time, you’ll be able to tell how much lactose your body can handle at once. 

• Choose dairy products that have less lactose. Not all dairy products contain the same amounts of lactose. For example, hard cheeses, especially Swiss, parmesan, and cheddar, are low in lactose. 

• Use lactose-free or lactose-reduced milk and milk products. There are many lactose-free or lactose-reduced products, including milk, yogurt, and cheeses. These are great options if you don’t want to give up dairy. 

• Consider lactase replacement enzymes. There are several lactase replacement enzymes available over the counter. Lactaid is a popular brand, but generics are also available. These enzymes are available as pills or liquids. You can add the liquid to milk, and it will break down all the lactose, making it safe for you to drink. You can also take a tablet before eating something with lactose. These enzymes don’t work for everyone, so you’ll have to try them to see if they’re an option for you. 

How do I know if a food contains lactose?

All types of milk contain lactose, so all dairy products will also contain lactose. You want to avoid any dairy-containing foods as well as any foods that have lactose added to them. You should avoid any foods that list the following terms on their ingredient list:

• Lactose

• Milk

• Nonfat dry milk powder

• Curds

• Whey

• Dry milk solids

Some ingredients that are made from milk do not contain lactose. The following ingredients do not have lactose and are safe to eat: 

• Casein

• Lactalbumin

• Lactate

• Lactic acid

About 20% of prescription medications and 6% of over-the-counter medications contain lactose. You can ask your pharmacist about the ingredients of your medications or check the package insert. But most people with lactose intolerance do not need to avoid medications that contain lactose: medications usually contain small amounts of lactose. Studies have shown that people can take these medications without having symptoms. 

Will I always have lactose intolerance?

Lactose intolerance caused by gastroenteritis or minor surgery will improve with time. Lactose intolerance caused by genetics and some medical conditions will not get better. In these cases, people will have lactose intolerance for their entire lives and may need to add calcium and vitamin D supplements to their diet. 

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Written by:

Meredith Grace Merkley, DO, FAAP

Dr. Merkley is a licensed, board-certified pediatrician who has over a decade of experience working in community health. She is currently a National Health Services Corp scholar, and is serving as the medical director of a school-based health clinic at a federally funded health center.

Edited by:

Patricia Pinto-Garcia, MD, MPH

Patricia Pinto-Garcia, MD, MPH, is a medical editor at GoodRx. She is a licensed, board-certified pediatrician with more than a decade of experience in academic medicine.

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