Lactose intolerance

Expert reviewer Paul Mcardle, Freelance Dietitian
Next review due August 2022

Lactose intolerance means your digestive system can’t break down lactose: a sugar found in milk from cows, sheep and goats. This can give you unpleasant symptoms such as bloating, diarrhoea and tummy cramps.

It’s quite a common problem but not everyone will have symptoms from it. There’s no cure, but most people can control their symptoms by being careful about what they eat and drink.

Young woman eating pizza

About lactose intolerance

Your body makes an enzyme called lactase, which breaks down lactose into simple sugars in your bowel. Your body can then absorb these simpler sugars into your bloodstream.

If your bowel doesn’t make enough lactase, you may develop symptoms after drinking milk or eating foods that have lactose in them. If lactose can’t be absorbed, it stays in your bowel which can make everything more liquid. When the lactose reaches the lower part of your bowel, bacteria start to break it down which causes gas.

Lactose intolerance usually affects older children and adults because the amount of lactase in your bowel reduces naturally as you get older.

In the UK, between one and two in every 10 people have lactose intolerance. It’s more common in places where milk isn’t such a big part of the usual adult diet, such as South America, Africa and Asia.

Symptoms of lactose intolerance

The symptoms of lactose intolerance usually start between a few minutes and a few 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. These may include:

  • feeling bloated
  • pain or cramps in your tummy (abdomen) or a rumbling tummy
  • diarrhoea
  • farting (passing wind)
  • feeling sick
  • feeling very tired
  • mouth ulcers

Symptoms can vary from mild to severe. How bad they are may depend on how much lactose you’ve had and 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 look a lot like the symptoms of other conditions, such as irritable bowel syndrome, ulcerative colitis and coeliac disease. If you have any of these symptoms for more than a few days contact your GP for advice.

Diagnosis of lactose intolerance

Your GP will ask about your symptoms and may examine your abdomen.

Your GP 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 not clear whether you have lactose intolerance after you’ve tried a lactose-free diet, your GP may refer you for further tests. These may include:

  • a lactose tolerance blood test
  • a hydrogen breath test, which measures the amount of hydrogen you breathe out after having lactose
  • a biopsy of your small bowel – this is a small sample of tissue taken from your bowel and looked at in a laboratory
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Treatment of lactose intolerance

There isn’t a cure for lactose intolerance. If it’s caused by another illness it should go away of its own accord (see our Causes section below). If not, you can usually control your symptoms by making changes to your diet. Some people may only need to cut down the amount of lactose they eat and drink, others may need to avoid it altogether. Milk and dairy products are the main sources of lactose.

If you have lactose intolerance, here are some tips to help you reduce your symptoms.

  • Hard cheeses, such as Cheddar, Edam and Parmesan, 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 yogurt without any problems. This may be partly because of the effects of the bacteria that are used to produce yogurt.
  • You can buy preparations of the enzyme lactase to take. These may help you if you eat foods containing lactose.
  • Watch out for lactose in some foods that you don’t expect to contain it, such as bread, cereals and some ready meals. Check the ingredients – the label should say whether a product contains lactose.
  • You may find you can tolerate milk if you have it with meals, rather than on its own.
  • You can buy milk and other products that contain a reduced amount of lactose. It’s important to remember that milk from goats and sheep contains lactose and so these aren’t suitable alternatives to cow’s milk.
  • 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 can’t eat any dairy foods, you may not be getting enough calcium in your diet. Non-dairy foods that contain calcium include green leafy vegetables, soya beans, tofu and sardines. 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.

You can get more tips and information about diet and lactose intolerance from the organisations listed in our Other helpful websites section below.

Causes of lactose intolerance

Lactose intolerance is caused by not having enough of an enzyme called lactase in your bowel. This is called lactase deficiency and there are four main types.

  • Primary lactase deficiency is the most common type of lactose intolerance. It happens when the amount of lactase in your bowel reduces over time, usually from about the age of two or three onwards.
  • Secondary lactase deficiency is when the lining of your bowel becomes damaged, usually because of a condition such as severe gastroenteritis or coeliac disease. It’s usually temporary and gets better once you’ve recovered from the condition that caused it.
  • Congenital lactase deficiency is very rare and it’s when a baby is born able to make very little or no lactase at all. If your baby has this condition, they won’t put on weight and will have diarrhoea. If your baby has these symptoms, you should see your GP as soon as you can.
  • Developmental lactase deficiency can develop in babies who are born early. It usually lasts for a short time after your baby is born and gets better as they get older.

Complications of lactose intolerance

Most people with lactose intolerance manage their condition well and have few problems. The main possible complications are developing conditions that affect your bones, such as osteoporosis, fractures and rickets. These can develop if you’re eating little or no dairy products and not getting enough calcium or vitamin D in your diet. Because of this, it’s important to take either supplements or natural sources of vitamin D and calcium if you’re lactose intolerant, as mentioned in the Treatment section above.

Frequently asked questions

  • No, they’re two different conditions, If your child has a milk allergy, their immune system responds to the milk they drink and produces an allergic reaction. In lactose intolerance your child’s immune system isn’t involved at all. Instead lactose intolerance develops because your body isn’t producing enough of the enzyme that breaks down lactose.

    Lactose intolerance tends to affect older children and adults, whereas milk allergy is much more common in babies and young children.

    If your child has an allergy to milk, their immune system mistakes some of the proteins found in milk as harmful. This leads to an allergic reaction. The reaction can happen quickly, with symptoms developing within a few minutes or hours. Or it can happen more slowly, with symptoms starting after a few hours or even days.

    The symptoms of cow’s milk allergy vary, depending on how severe the reaction is and what kind of allergic response is happening.

    The symptoms that develop quickly may include:

    • itchy, red skin and a rash
    • being short of breath and wheezing
    • swollen lips and face, including around the eyes
    • being sick and feeling sick
    • cramping pains in the abdomen (tummy)
    • diarrhoea

    Symptoms that may develop more slowly include:

    • liquid or very soft poo and pooing more often
    • blood or mucus in poo
    • being short of breath and wheezing
    • red itchy skin or eczema
    • tummy pain or colic
    • not wanting to eat or refusing food
    • constipation

    Babies with a cow’s milk allergy usually start having symptoms in their first few months, and almost always by the end of the first year. Most children grow out of milk allergy by the time they reach adulthood.

    Very rarely, a baby with milk allergy can have a severe reaction called anaphylaxis. The symptoms can sometimes be difficult to spot, but include drooling, being sick, scratching, drowsiness and shortness of breath.

    Anaphylaxis is an emergency and needs treating immediately. So if this happens, or you’re worried about your baby, get medical help straightaway.

    If you or your child feels unwell after drinking milk or eating dairy products, or you’re worried your child may have an allergy contact your GP. Babies with a cow’s milk allergy may be given a special milk formula called hydrolysed milk. Goat’s milk and sheep’s milk can trigger an allergic reaction too, so can’t be used in place of cow’s milk if your child has an allergy.

  • Lactose is sometimes added to medicines to bulk them out and can also be added to inhaled powders, sugar coatings and liquid medicines. This includes medicines that you buy over the counter or get on prescription and includes some complementary medicines.

    The amount of lactose in most medicines is small, usually less than 2g (a glass of milk has about 12–15g). That means that most people are unlikely to develop symptoms after taking a medicine that has lactose in it. If you have a severe lactose intolerance, ask your doctor to check how much lactose there is in any medicine you take. They can do this by contacting the manufacturer.

    If you’re concerned about lactose intolerance and any medicine you’re taking, talk to your GP or pharmacist for advice.

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Related information

    • Lactose intolerance. PatientPlus., last edited December 2016
    • Nutrition in gastrointestinal diseases. Oxford Handbook of Nutrition and Dietetics (online). Oxford Medicine, updated December 2015
    • Lactase deficiency. BMJ Best Practice., last reviewed April 2019
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    • Vitamin D. British Dietetic Association., reviewed August 2016
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  • Reviewed by Graham Pembrey, Lead Editor, Bupa UK Content Team
    Expert reviewer Paul McArdle, Freelance Dietitian
    Next review due August 2022