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Lactose intolerance

Lactose intolerance means your body can’t break down lactose (a sugar mainly found in milk).

Lactose is a sugar found in milk and other dairy products. An enzyme (a type of chemical) called lactase, which is produced by your small bowel, breaks lactose down into two simpler sugars (glucose and galactose). Once lactose has been broken down, it's absorbed from your bowel into your bloodstream.

If your body doesn’t make enough lactase, you may develop symptoms of lactose intolerance. Lactose intolerance usually affects older children and adults because the level of lactase starts to decrease naturally as you get older.

In the UK, around five in 100 people have lactose intolerance. It’s more common in countries where milk isn't part of the usual adult diet, such as South America, Africa and Asia.

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  • Symptoms Symptoms of lactose intolerance

    The symptoms of lactose intolerance can occur after you’ve eaten or drunk something that contains lactose. Symptoms of lactose intolerance may include:

    • feeling bloated
    • pain or cramps in your tummy (abdomen)
    • diarrhoea
    • wind
    • feeling sick

    These symptoms may be caused by problems other than lactose intolerance. If you have any of these symptoms for more than a few days see your GP for advice.

  • Diagnosis Diagnosis of lactose intolerance

    Your GP will ask about your symptoms and examine you. He or she may ask you to keep a diary of your symptoms and what you eat and drink on a day-to-day basis. This will help your GP to look for any links between your symptoms and your diet.

    Your GP may suggest you completely remove foods and drinks containing lactose from your diet for a trial period of two weeks. 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.

    If you think your child may have symptoms of lactose intolerance, your GP may ask for a sample of his or her faeces (stool sample). This will be sent away for testing to check if your child’s body is absorbing lactose.

    Having specific tests to diagnose if you have lactose intolerance is uncommon. However, if there is uncertainty about your diagnosis, your GP may refer you to have one or more of the following tests.

    • Hydrogen breathe test. After you’ve drunk some milk, the level of hydrogen (a type of gas) in your breath will be measured. Lactose intolerance can cause the bacteria in your bowel to produce more hydrogen than normal. Therefore, if there’s a large amount of hydrogen in your breath, this may be a sign that you have lactose intolerance. 
    • A lactose tolerance blood test. Your doctor will take a blood sample after you’ve had some lactose by mouth to measure your blood sugar (glucose) level. If your blood sugar level increases by a small amount or not at all, this suggests that your body hasn’t digested or absorbed the lactose. This is a sign that you may have lactose intolerance.
    • Biopsy. If your diagnosis is uncertain you may need to have a biopsy (a small sample of tissue) taken from the lining of your small bowel. This is done using a narrow, flexible, tube-like instrument called an endoscope. The sample will be sent to a laboratory to be tested for lactase.
  • Treatment Treatment of lactose intolerance

    There isn’t a cure for lactose intolerance, but you can control your symptoms. Milk and dairy products are the main sources of lactose and cutting down how much of these products you have may help your symptoms. We’ve put together some tips to help you with this.

    • Hard cheeses, such as Cheddar, Edam and Parmesan, only contain a small amount of lactose. Therefore, you may be able to eat these without having any symptoms.
    • You may also find that you can eat yoghurt without any problems. This is thought to be partly because of the effects of the bacteria that are used to produce yoghurt.
    • You can also buy lactase preparations to take if you eat foods containing lactose.
    • There may be lactose in some foods that you don’t expect to contain it, for example bread, cakes, cereals, margarine and some ready meals. Check the ingredients as the label should say whether a product contains lactose.
    • You may be able to have some milk (about 200ml – a small glass) without reacting to it. You could try having small amounts of milk to find out how much you can drink without getting any symptoms.
    • 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 ask your GP for advice and read the patient information leaflet that comes with your medicine.

    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 nuts. Talk to your GP about your diet if you have any questions. He or she may refer you to a dietitian for help and support. Your GP may also recommend that you take calcium and vitamin D supplements.

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  • Causes Causes of lactose intolerance

    Lactase deficiency is when your body doesn’t produce enough lactase, which can lead to symptoms of lactose intolerance.

    There are three main types of lactase deficiency.

    • Primary lactase deficiency is caused by an inherited faulty gene that runs in families. It can occur at different ages.
    • Secondary lactase deficiency is when the lining of your bowel becomes damaged by a separate condition such as gastroenteritis. This may reduce the amount of lactase that your body makes. Secondary lactase deficiency is usually temporary and gets better once you have recovered from the condition that caused it. 
    • Congenital lactase deficiency is a condition that also runs in families, but it’s very rare. It can cause you to produce little or no lactase from birth, and if left untreated, it can lead to serious complications. To find out more about congenital lactase deficiency see our FAQ.
  • Complications Complications of lactose intolerance

    If you have lactose intolerance, you can control your symptoms by reducing the amount of lactose in your diet. However, the lack of dairy products in your diet will mean you need to get vitamin D and the mineral calcium, from other sources. If you don’t get enough calcium in your diet, your bones may become weak and you may develop a condition known as osteopenia.

    Babies born with the rare but more severe form of lactose intolerance may not grow as they should if they don’t receive the right nutrients. They will need to be fed a lactose-free formula from birth.

  • FAQs FAQs

    Is lactose intolerance the same as a milk allergy?


    No. If you have lactose intolerance, it means your body can’t break down a sugar in milk called lactose. If you have a milk allergy, it means you're allergic to some of the proteins found in milk.


    Lactose intolerance and milk allergy can be confused because the symptoms of both occur after eating or drinking dairy products.

    If you have lactose intolerance, it means your body doesn’t have enough lactase. This is an enzyme (a type of chemical) that your body needs to break down the lactose in milk. If lactose isn’t broken down, it can cause symptoms, such as diarrhoea and bloating.

    If you have an allergy to milk, your body mistakes some of the proteins found in milk as harmful, leading to an allergic reaction.

    The symptoms of milk allergy are often mild and may be similar to those of lactose intolerance. For example, you may get pain in your tummy (abdomen) and diarrhoea. However, some allergic reactions can be severe (anaphylaxis) and your symptoms might include:

    • a swollen tongue or throat
    • sudden wheezing, tightness in your chest or difficulty breathing
    • dizziness
    • a hoarse voice

    Lactose intolerance tends to affect older children and adults, whereas milk allergy is much more common in babies and young children. It's important to determine which one you have, because of the risk of a severe allergic reaction.

    If you or your child feels unwell after drinking milk or eating dairy products, see your GP. Don't cut milk or dairy products out of your or your child's diet without talking to your GP first. Babies with a cow’s milk allergy may be given a special formula. It’s important to remember that milk from goats and sheep contains lactose and so these aren’t suitable alternatives to cow’s milk.

    Can babies be born with lactose intolerance?


    It's possible, but it's very rare for babies to be born with lactose intolerance.


    Some babies may be born without any lactase in their bodies, but it’s very rare. The condition is known as congenital lactase deficiency.

    If your baby has congenital lactase deficiency, he or she may develop diarrhoea when they drink milk (breast milk or formula milk) that contains lactose.

    The only treatment for congenital lactase deficiency is to remove lactose from your baby’s diet from birth. Your GP will refer you to a specialist to confirm the diagnosis and arrange for you and your baby to see a dietitian. A dietitian can help ensure your baby’s diet is lactose-free. Your baby will probably need to take calcium and vitamin D supplements.

    Lactose overload can sometimes be mistaken for lactose intolerance in babies. This can occur if your baby drinks a large amount of milk that he or she can’t digest. Lactose overload can cause pain in your baby’s tummy (abdomen) and very frequent bowel movements.

    If your baby seems to be having problems with feeding or is having symptoms such as diarrhoea, see your GP. Don't stop breastfeeding or giving your baby milk without seeing your GP first.

    Can I drink soya milk if I have lactose intolerance?


    Yes, as soya milk doesn't contain lactose.


    Although there isn’t a cure for lactose intolerance, you can control your symptoms by reducing the amount of lactose in your diet. One way of doing this is by drinking soya milk instead of cow, sheep or goat milk, as it doesn't contain any lactose.

    It's important not to completely cut out dairy products from your diet unless you're very sensitive to lactose. This is because these foods are an important source of calcium and vitamin D. Calcium is important to keep your bones healthy. If you want to drink soya milk as an alternative, it's a good idea to choose a product that has added calcium.

    If you need more information, ask your GP for advice.

  • Resources Resources

    Further information


    • Lactose intolerance. PatientPlus., published 10 December 2013
    • Food allergy and food intolerance. PatientPlus., published 20 April 2011
    • Pediatric lactose intolerance. Medscape., published 20 December 2013
    • Lactose intolerance. Medscape., published 15 March 2013
    • Lactose intolerance. Food Standards Agency., accessed 19 May 2014
    • Lactose intolerance. British Nutrition Foundation., published September 2009
    • Bone and joint health – diet and bone health. British Nutrition Foundation., published July 2009
    • Eadala P, Waud J, Matthews S, et al. Quantifying the hidden lactose in drugs used for the treatment of gastrointestinal conditions. Aliment Pharmacol Ther 2009; 29(6):677–87. doi: 10.1111/j.1365-2036.2008.03889.x
    • Milk allergy and intolerance, Reduced lactose or lactose free. Food Standards Agency., accessed 19 May 2014
    • Milk Allergy. Allergy UK., published December 2013
    • Anaphylaxis and severe allergic reactions. Allergy UK., published March 2012
    • Lactose intolerance. CORE., published November 2005
    • Martin, EA. Concise colour medical dictionary. 3rd ed. Oxford: Oxford University Press 2002: 232 
    • Lactase deficiency. BMJ Best Practice., published 15 January 2014
    • Lactose overload in babies. Australian Breastfeeding Association., published October 2012
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