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Lactose intolerance

Expert reviewer, Louise McKenna, Specialist Dietitian, Cromwell Hospital
Next review due January 2025

Lactose intolerance means your digestive system has trouble breaking down lactose – a sugar found in milk and dairy products. This can give you unpleasant symptoms, such as bloating, diarrhoea and tummy cramps.

There’s no cure for lactose intolerance, but most people can control their symptoms by being careful about what they eat and drink.

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About lactose intolerance

If you have lactose intolerance, your body doesn’t make enough (or sometimes any) of a substance called lactase. This is known as lactase deficiency. Lactase is needed to break down lactose from milk into simpler sugars in your bowel, which can then be absorbed into your bloodstream. If there isn’t enough lactase in your bowel, your body can’t digest and absorb lactose, leading to the symptoms of lactose intolerance.

People with lactose intolerance most often develop it during childhood or early adulthood. This is because babies normally have high levels of lactase, which reduces naturally as you get older. But lactose intolerance can sometimes affect babies too. See Causes section below for more information. Lactose intolerance is different from a milk allergy, which is something that more commonly affects babies and young children. If you have a milk allergy, your immune system has an allergic response against the proteins in milk.

In the UK, around one in every 10 older children and adults are thought to have lactose intolerance. It’s more common in places in certain areas of the world, such as South America, Africa and Asia.

Causes of lactose intolerance

There are four main types of lactose intolerance, that develop in different ways.

  • Primary lactose intolerance is lactose intolerance that develops on its own, over time. This happens naturally in some people, as their levels of lactase reduce after early childhood.
  • Secondary lactose intolerance is caused by damage to the lining of your bowel. This is usually because of a condition, such as severe gastroenteritis, inflammatory bowel disease (IBD) or coeliac disease. It’s usually temporary and gets better once you’ve recovered from the condition that caused it.
  • Congenital lactose intolerance is when a baby is born with little or no ability to make lactase at all. It’s a very rare and serious condition in babies that needs urgent treatment.
  • Developmental lactose intolerance is something that can affect babies who are born early (premature). It usually quickly gets better as they get older and their bowel develops.

Symptoms of lactose intolerance

The symptoms of lactose intolerance usually start between a few minutes and a couple of hours after you’ve eaten or drunk something that contains lactose. For some people it can take up to 12 hours for symptoms to develop. Symptoms may include:

  • feeling bloated
  • pain or cramps in your tummy (abdomen)
  • ‘rumbling’ noises in your tummy
  • diarrhoea
  • flatulence (‘farting’ or passing wind)
  • feeling sick

Some people have more general symptoms too, such as feeling very tired or having aching joints and muscles. Symptoms can vary from mild to severe. How bad they are may depend on how much lactose you’ve had, as well as how high your own individual tolerance is. People with lactose intolerance vary in the amount of lactose they can have before any symptoms start. Most people can have up to a glass of milk every day without having symptoms.

The symptoms of lactose intolerance can be very similar to the symptoms of other conditions, such as irritable bowel syndrome, ulcerative colitis and coeliac disease. If you get these symptoms regularly, contact a GP for advice.

Diagnosis of lactose intolerance

When you see a GP with symptoms affecting your bowel, they’ll want to ask you some questions and may examine your abdomen.

They may ask you to try a strict lactose-free diet for two weeks. This means completely removing food and drink containing lactose from your diet. If your symptoms get better during this time, but come back when you start having lactose again, it’s likely that you have lactose intolerance.

You probably won’t need any other tests to diagnose lactose intolerance. But if it’s still not clear whether you have lactose intolerance, your GP may refer you for further tests. These may include:

  • a hydrogen breath test, to test for increased levels of hydrogen in your breath after having lactose – a sign of lactose intolerance 
  • a lactose tolerance blood test, to check whether your blood glucose increases after you have lactose
  • a biopsy of your small bowel – this involves taking a small sample of tissue from your bowel to measure how much lactase it contains
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Treatment of lactose intolerance

If lactose intolerance is caused by another illness, it should go away once the underlying illness is treated.

Primary lactose intolerance (that doesn’t have an underlying cause) doesn’t have a cure. It’s something that you will have for life. But there are ways to manage your symptoms. 

Lactose intolerance diet

You can often control your symptoms by making changes to your diet. Most people can tolerate a small amount of lactose, so only need to cut down the amount of lactose they eat and drink. Some people may need to avoid it altogether. Milk and dairy products are the main sources of lactose. But they’re also good sources of calcium. It’s important to include suitable alternatives in your diet and not exclude foods unless you need to.

Here are some tips to help.

  • Hard cheeses, such as Cheddar, Edam and Parmesan, are high in calcium but only contain a small amount of lactose. So you may be able to eat these without having any symptoms.
  • You may also find that you can eat certain yogurts without any problems. This may be partly because of the effects of the bacteria that are used to produce yogurt.
  • There might be lactose in some foods that you don’t expect, such as some breads, cereals and ready meals. Check the ingredients – the label may say whether a product contains lactose. Or, you can check if it contains milk or milk products.
  • You may find you can tolerate milk if you have it with meals, rather than on its own.
  • You can buy lactose-free alternatives, such as soya milk, almond milk and oat milk. There are also lactose-free dairy products that have been modified to have a reduced amount of lactose. Aim to choose products that have been fortified with calcium and iodine.
  • Some medicines may contain lactose. Always read the patient information leaflet that comes with your medicine and ask your pharmacist if you have any queries.
  • If you’re restricting dairy foods in your diet, aim to eat plenty of non-dairy foods that contain calcium. These include green leafy vegetables, soya beans, tofu and sardines.

You may need to experiment a bit with different foods, to find out how much lactose you can tolerate before getting symptoms. Talk to your GP about your diet if you’re concerned. They may refer you to a dietitian for help and support. Your GP may also recommend that you take calcium and vitamin D supplements.

Lactase supplementation

You can buy supplements of lactase, which will help to break down any lactose in your diet and may reduce your symptoms. These may be added to milk products, or you may take them separately as tablets.

Complications of lactose intolerance

Most people with lactose intolerance are able to manage their symptoms by controlling their diet, and have few problems. However, if you reduce or restrict dairy products, you may not get enough calcium or vitamin D in your diet. This increases your risk of developing conditions that affect your bones, such as osteoporosis, fractures and rickets. Because of this, it’s important to monitor your intake and seek medical advice if you feel you may not be getting enough. Taking supplements of vitamin D and calcium may help.

Frequently asked questions



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Related information

  • Discover other helpful websites

    • Lactose intolerance. Encyclopaedia Britannica. www.britannica.com, accessed 24 November 2021
    • Lactose intolerance. Medscape. emedicine.medscape.com, updated 4 December 2019
    • Lactase deficiency. BMJ Best Practice. bestpractice.bmj.com, last revised 24 October 2021
    • Cow's milk allergy in children. NICE Clinical Knowledge Summaries. cks.nice.org.uk, last revised August 2021
    • torhaug CL, Fosse SK, Fadnes LT. Country, regional, and global estimates for lactose malabsorption in adults: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol 2017; 2(10):738–46. doi: 10.1016/S2468-1253(17)30154-1
    • Misselwitz B, Butter M, Verbeke K, et al. Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management. Gut 2019; 68(11):2080–91. doi:10.1136/gutjnl-2019-318404
    • Calcium. British Dietetic Association, June 2021. www.bda.uk.com
  • Reviewed by Pippa Coulter, Freelance Health Editor, January 2022
    Expert reviewer Louise McKenna, Specialist Dietitian, Cromwell Hospital
    Next review due January 2025

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