Lactose Intolerance: Symptoms, Causes, Diagnosis, and Treatment Guide
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 17, 2026
Lactose intolerance is difficulty digesting the sugar in milk and dairy products because the small intestine doesn't make enough of the enzyme lactase. Diarrhea, gas, bloating, and cramps usually start within a few hours of eating dairy. The condition is usually harmless, and most people can manage it with smaller servings, lactose-reduced products, or lactase tablets without giving up dairy entirely [1][2].
Quick Answer: What is lactose intolerance and how is it treated?
Lactose intolerance is a shortage of lactase, the enzyme that breaks down milk sugar, so undigested lactose causes diarrhea, gas, bloating and cramps within a few hours of eating dairy. It is not an allergy. A hydrogen breath test confirms it. Most people manage with smaller dairy servings, hard cheeses, yogurt, lactose-free products and lactase tablets while getting enough calcium. [1] [2]
What the research says
Most adults with lactose intolerance can handle about a cup of milk. A systematic review of 36 randomized studies found moderate-quality evidence that 12 to 15 g of lactose (roughly 1 cup of milk) is well tolerated by most adults. The evidence for probiotics and for gradually building tolerance was insufficient, and most studies enrolled people with lactose malabsorption rather than symptomatic intolerance (Shaukat et al., Ann Intern Med, 2010 [3]).
Yogurt is digested better than other dairy sources. A review of the studies in lactose-intolerant people found that the lactose in yogurt is digested more efficiently because the live bacteria in it (about 10^8 bacteria per mL of Lactobacillus bulgaricus and Streptococcus thermophilus) supply lactase that survives the stomach and keeps working in the small intestine (Savaiano, Am J Clin Nutr, 2014 [4]).
Whether you get symptoms depends on more than lactase. A Gut review explains that the likelihood of symptoms depends on the lactose dose, lactase levels, and the gut microbiome, that people with visceral hypersensitivity or irritable bowel syndrome are more likely to react, and that low-lactose diets and lactase supplements have only modest effects because lactose is one of several poorly absorbed carbohydrates (Misselwitz et al., Gut, 2019 [5]).
What Is Lactose Intolerance?
Lactose intolerance is a condition that makes it hard to digest lactose, the sugar in milk and milk products. It develops when the small intestine produces too little of an enzyme called lactase. Low lactase levels don't automatically mean intolerance: someone can have reduced lactase and still digest milk products. The condition appears only when lactase levels fall too low [1].
The condition is usually harmless, but its symptoms of diarrhea, gas, and bloating after eating or drinking lactose-containing foods can be uncomfortable. The good news is that most people can manage it without giving up all dairy foods [1].
How Your Body Normally Digests Milk Sugar
Lactase in the small intestine splits lactose into two simple sugars, glucose and galactose.
The intestinal lining absorbs these simple sugars into the bloodstream.
The body uses them for energy, like other sugars.
When lactase is insufficient, the process breaks down at step 1. Undigested lactose moves into the colon instead of being absorbed, and bacteria in the colon interact with it. That interaction causes the symptoms of lactose intolerance [1].
Normal digestion versus lactose intolerance: without enough lactase, undigested lactose reaches the colon and causes gas, bloating, and diarrhea.
What are the symptoms of lactose intolerance?
Symptoms usually begin within a few hours after eating or drinking foods that contain lactose. Noticing that symptoms follow dairy is often the first clue [1].
Diarrhea: one of the most common symptoms.
Bloating: abdominal fullness after lactose reaches the colon.
Gas: caused by colon bacteria interacting with undigested lactose.
Stomach cramps: from mild discomfort to painful cramping.
Nausea: sometimes accompanied by vomiting.
When should you see a doctor about lactose intolerance?
Make an appointment with a healthcare professional if you often have symptoms of lactose intolerance after eating dairy foods, especially if you're worried about getting enough calcium [1]. A visit is also worthwhile because other conditions can cause similar symptoms, and confirming the cause helps you treat the right problem instead of cutting out foods you might tolerate.
What Causes Lactose Intolerance?
Lactose intolerance happens when the small intestine doesn't produce enough lactase. It is not caused by an allergy and is not the same as a milk protein allergy; it is specifically a shortage of the enzyme needed to break down milk sugar. There are three types, each with a different cause of the lactase deficiency [1].
Type | How it develops | How common |
|---|---|---|
Primary lactose intolerance (lactase non-persistence) | Lactase production falls off sharply by adulthood, even though enough is made at birth. | The most common type |
Secondary lactose intolerance | The small intestine makes less lactase after an illness, injury, or surgery. | Less common; may improve when the cause is treated |
Congenital or developmental lactose intolerance | Babies are born with a lactase deficiency, or premature infants have not yet developed enough lactase-producing cells. | Rare |
Primary Lactose Intolerance
People with primary lactose intolerance produce enough lactase at birth, which infants need because all their nutrition comes from milk. As children replace milk with other foods, lactase production typically drops, but in most people it stays high enough to digest the dairy in a standard adult diet. In primary lactose intolerance, lactase production falls off sharply by adulthood, making milk products hard to digest [1].
Secondary Lactose Intolerance
This form develops when the small intestine decreases lactase production after an illness, injury, or surgery involving the small intestine. Conditions linked to it include intestinal infection, celiac disease, bacterial overgrowth, and Crohn's disease. Treating the underlying condition may restore lactase levels and improve symptoms, although it can take time [1].
Congenital or Developmental Lactose Intolerance
It is possible, but rare, for babies to be born with lactose intolerance caused by a lack of lactase. It is inherited in an autosomal recessive pattern, meaning both parents must pass on the same gene variant for a child to be affected. Premature infants can also have reduced lactase, because the small intestine doesn't develop lactase-producing cells until late in the third trimester [1].
What are the risk factors for lactose intolerance?
Lactose intolerance is more likely with increasing age, African, Asian, Hispanic or American Indian descent, and premature birth.
Risk factor | Why it increases risk |
|---|---|
Increasing age | It usually appears in adulthood and is not common in babies and young children. |
Ethnicity | Most common in people of African, Asian, Hispanic, and American Indian descent. |
Premature birth | Lactase-producing cells develop late in the third trimester, so premature infants may have less lactase. |
Diseases of the small intestine | Bacterial overgrowth, celiac disease, and Crohn's disease can cause the condition. |
Certain cancer treatments | Radiation therapy for cancer in the stomach, or intestinal complications from chemotherapy, raises the risk. |
What complications can lactose intolerance cause?
Lactose intolerance itself doesn't damage the digestive system or turn into a more serious disease. Its main complication is nutritional: people who cut out all dairy without a plan can fall short on calcium and vitamin D, the nutrients milk products typically supply [2].
How is lactose intolerance diagnosed?
Lactose intolerance is often suspected from symptoms and the response to cutting back on dairy, and a hydrogen breath test can confirm it. A hydrogen breath test can confirm the diagnosis [2]:
You drink a liquid that contains a high level of lactose.
The amount of hydrogen in your breath is measured at regular intervals.
Breathing out too much hydrogen means you aren't fully digesting and absorbing lactose, which confirms the condition.
What are the treatment options for lactose intolerance?
Lactose intolerance treatment depends on the cause, ranging from treating an underlying condition to following a low-lactose diet. If lactose intolerance stems from an underlying condition, treating that condition might restore your ability to digest lactose, although this can take months. For other causes, you can avoid the discomfort by following a low-lactose diet [2]. There are four main ways to lower the lactose in your diet:
Strategy | How it works |
|---|---|
Limit milk and other dairy products | Reduces your overall lactose intake. |
Small servings with meals | Include small servings of dairy in your regular meals. |
Lactose-reduced products | Choose lactose-reduced milk and ice cream. |
Lactase enzyme supplements | Add a liquid or powder lactase enzyme to milk to break down the lactose. |
Practical ways to lower the lactose in your daily diet while still enjoying dairy.
What self-care and lifestyle changes help lactose intolerance?
With some trial and error, you can predict how your body responds to foods that contain lactose and work out how much you can eat or drink without discomfort. Few people have intolerance so severe that they must cut out all milk products or avoid nondairy foods and medicines that contain lactose [2].
Maintain Good Nutrition
Reducing dairy doesn't mean you can't get enough calcium. Many other foods supply it [2]:
Calcium source | Examples |
|---|---|
Vegetables | Broccoli and leafy green vegetables |
Fortified products | Calcium-fortified cereals and juices |
Fish | Canned salmon or sardines |
Milk substitutes | Soy milk and rice milk |
Fruit | Oranges |
Nuts and beans | Almonds, Brazil nuts, and dried beans |
Dairy-free calcium sources, plus vitamin D from eggs, yogurt, and sunlight.
Also make sure you get enough vitamin D, which is typically supplied by fortified milk. Eggs, liver, and yogurt also contain vitamin D, and your body makes it when you spend time in the sun. Even without restricting dairy, many adults don't get enough vitamin D, so talk to your healthcare professional about vitamin D and calcium supplements [2].
Limit Dairy Products Smartly
Most people with lactose intolerance can enjoy some milk products without symptoms. You might tolerate low-fat products such as skim milk better than whole-milk products, and you may be able to build tolerance by gradually adding dairy back into your diet [2]. Tactics that can minimize symptoms:
Tactic | Why it helps |
|---|---|
Smaller servings | Sip small servings of milk, up to 4 ounces (118 mL) at a time. The smaller the serving, the less likely it is to cause problems. |
Save milk for mealtimes | Drinking milk with other foods slows digestion and may lessen symptoms. |
Try different dairy products | Lactose content varies. Hard cheeses such as Swiss or cheddar have small amounts and generally cause no symptoms, and yogurt is often tolerated because its culturing bacteria naturally produce the enzyme that breaks down lactose. |
Buy lactose-reduced or lactose-free products | They are available in the dairy section of most supermarkets. |
Use lactase enzyme tablets or drops | Nonprescription products (such as Lactaid) can be taken just before a meal or added to milk, but they don't help everyone. |
Ice cream and milk contain the most lactose, but the high fat content of ice cream may let some people eat it without symptoms [2].
Can alternative medicine help lactose intolerance?
Probiotics are living organisms in your intestines that help maintain a healthy digestive system. They are also available as live cultures in some yogurts and as capsule supplements. They are sometimes used for digestive conditions such as diarrhea and irritable bowel syndrome and might help your body digest lactose. They are generally considered safe and may be worth trying if other methods don't help, although the research on whether they relieve lactose intolerance symptoms is limited [2][3].
How should you prepare for a lactose intolerance appointment?
If your symptoms suggest lactose intolerance, start by seeing your healthcare team [2].
What You Can Do
When you make the appointment, ask whether you need to do anything in advance, such as restricting your diet. Before the visit, make a list of:
Your symptoms, including any that seem unrelated to the reason for the appointment, and when they occur.
All medicines, vitamins, or other supplements you take, including doses.
Questions to ask your healthcare professional.
Useful questions include:
Are there other possible causes for my symptoms besides lactose intolerance?
What tests do I need?
What are my treatment options?
Must I stop eating all dairy products?
How can I be certain that I'm getting enough calcium in my diet?
Should I see a dietitian?
I have these other health conditions. How can I best manage them together?
Are there brochures or other printed material I can have? What websites do you recommend?
What You Can Do in the Meantime
Keep track of your daily servings of dairy foods, such as milk, ice cream, yogurt, and cottage cheese, including when you have them and what you eat with them. Tell your healthcare team which dairy foods, and in what amounts, give you symptoms, because this information can help with the diagnosis. You can also try cutting dairy products from your diet for a few days to see whether your symptoms ease, and let your healthcare professional know if they got better on the days you didn't have dairy [2].
What is the bottom line on lactose intolerance?
Lactose intolerance is common, manageable, and usually harmless. It stems from too little lactase in the small intestine and typically appears in adulthood, especially among people of African, Asian, Hispanic, and American Indian descent. Symptoms usually show up within a few hours of eating dairy and can be confirmed with a simple hydrogen breath test.
You don't need to give up dairy entirely. Smaller servings, milk at mealtimes, hard cheeses, yogurt, lactose-free products, and lactase enzyme supplements let most people enjoy food comfortably while keeping their calcium and vitamin D intake on track.
Your next step: start a symptom and food diary today and book an appointment to confirm what is really going on. Knowing your tolerance is the first step to eating comfortably again.
Frequently Asked Questions
What is lactose intolerance?
Lactose intolerance is a condition that makes it hard to digest lactose, the sugar in milk and milk products, because the small intestine doesn't make enough of the enzyme lactase. It usually causes diarrhea, gas, and bloating after eating dairy, but it is generally harmless and manageable.
What are the symptoms of lactose intolerance?
Symptoms usually begin within a few hours of eating or drinking foods that contain lactose. They include diarrhea, bloating, gas, stomach cramps, and nausea, sometimes with vomiting.
What causes lactose intolerance?
Lactose intolerance happens when the small intestine doesn't produce enough lactase, the enzyme that splits lactose into glucose and galactose. Undigested lactose moves into the colon, where bacteria interact with it and cause symptoms.
What is the most common type of lactose intolerance?
Primary lactose intolerance (lactase non-persistence) is the most common type. People make enough lactase at birth, but production falls off sharply by adulthood, making milk products hard to digest.
Can lactose intolerance go away?
If it is caused by an underlying condition such as celiac disease, an intestinal infection, or Crohn's disease, treating that condition may restore lactase levels, although this can take months. Primary, age-related lactase decline does not reverse.
How is lactose intolerance diagnosed?
A healthcare professional may suspect it from your symptoms and your response to cutting back on dairy. A hydrogen breath test can confirm it: after you drink a high-lactose liquid, too much hydrogen in your breath means you aren't fully digesting and absorbing lactose.
Do I have to give up all dairy with lactose intolerance?
No. Few people are so intolerant that they must cut out all milk products. Most can manage with smaller servings (up to 4 ounces at a time), dairy with meals, hard cheeses, yogurt, and lactose-free products.
What foods can I eat to get enough calcium without dairy?
Good sources include broccoli and leafy greens, calcium-fortified cereals and juices, canned salmon or sardines, soy and rice milk, oranges, and almonds, Brazil nuts, and dried beans.
Do lactase enzyme tablets really work?
Over-the-counter lactase tablets or drops (such as Lactaid) can help you digest dairy when taken just before a meal or added to milk, but they don't help everyone with lactose intolerance.
Is yogurt okay with lactose intolerance?
Many people tolerate yogurt because the bacteria used to culture it naturally produce the enzyme that breaks down lactose. Hard cheeses such as Swiss or cheddar also contain little lactose and generally cause no symptoms.
Related Reading
Hydrogen Breath Test: How to Prepare, What Happens and What Results Mean explains the breath test used to diagnose sugar intolerances and small intestinal bacterial overgrowth (SIBO).
External Resources
References
Mayo Clinic Staff. Lactose intolerance: symptoms & causes. Mayo Clinic. September 22, 2025. https://www.mayoclinic.org/diseases-conditions/lactose-intolerance/symptoms-causes/syc-20374232
Mayo Clinic Staff. Lactose intolerance: diagnosis & treatment. Mayo Clinic. September 22, 2025. https://www.mayoclinic.org/diseases-conditions/lactose-intolerance/diagnosis-treatment/drc-20374238
Shaukat A, Levitt MD, Taylor BC, et al. Systematic review: effective management strategies for lactose intolerance. Annals of Internal Medicine. 2010;152(12):797-803. PMID 20404262. https://doi.org/10.7326/0003-4819-152-12-201006150-00241
Savaiano DA. Lactose digestion from yogurt: mechanism and relevance. American Journal of Clinical Nutrition. 2014;99(5 Suppl):1251S-1255S. PMID 24695892. https://doi.org/10.3945/ajcn.113.073023
Misselwitz B, Butter M, Verbeke K, et al. Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management. Gut. 2019;68(11):2080-2091. PMID 31427404. https://doi.org/10.1136/gutjnl-2019-318404
Medical disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. The clinical information in this guide reflects source material last updated in September 2025.
Comments