Symptoms of lactose intolerance can start a few minutes, or a few hours, after having food or drink containing lactose.
Common symptoms of lactose intolerance include:
- tummy pain or discomfort
- bloating
- farting
- tummy rumbling
- diarrhoea or constipation
- feeling sick or being sick
You may also have some other symptoms that are not related to your digestive system, such as headaches, tiredness and joint or muscle pain.
Foods that contain lactose
Lactose is found in foods containing animal milk (dairy products), including milk from cows, goats and sheep.
Dairy products include:
- milk
- butter
- cheese
- cream
- yoghurt
- ice cream
Many processed foods can also contain lactose, including:
- muesli and breakfast cereals containing chocolate
- baked foods like bread, crackers, cakes, biscuits and pastry
- sauces and salad dressings
- diet and protein shakes
Find out more about lactose intolerance and checking food labels on the Allergy UK website.
Food allergy
A food intolerance is different from having a food allergy. Food allergies can cause symptoms such as difficulty breathing, itchy skin, and swelling of the lips, face and eyes. A food allergy can be life threatening.
Some symptoms of lactose intolerance are common, but get medical help if they keep happening or do not go away.
See a GP if:
You have symptoms of lactose intolerance and:
- your symptoms keep coming back and often happen after eating
- you've noticed changes in your poo that are not usual for you, such as looser poo, pooing more often or constipation for 3 weeks
- you've had blood in your poo for 3 weeks
- you've had tummy bloating and discomfort for 3 weeks
- you've been losing weight without trying
Call 999 if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised or itchy.
These can be signs of a serious allergic reaction (anaphylaxis). Anaphylaxis needs immediate treatment in hospital.
If a GP thinks you have lactose intolerance, you may:
- be asked to follow a lactose elimination diet – where you stop eating foods containing lactose to see if your symptoms improve
- have blood tests
- do a hydrogen breath test – where hydrogen gas in your breath is measured to find out how well you digest lactose
If your symptoms are severe and do not get better, you may need a gastroscopy. This is where a long, thin, flexible tube is passed into your mouth and down into your stomach. A very small sample of cells may be taken from your small intestine so it can be tested.
Before the test, you may be given painkillers to help with any discomfort and a sedative to help you relax.
For most people with lactose intolerance, the symptoms can be prevented by reducing the amount of food you eat that contains lactose or by avoiding these foods completely.
But it's important not to cut foods out of your diet or your child's diet without the advice of a GP or a food and nutrition specialist (dietitian).
Taking a lactase supplement before having food or drink containing lactose may reduce or prevent symptoms for some people.
In some people, lactose intolerance is caused by another health condition, such as coeliac disease. Treating the underlying cause should help.
The most common cause of lactose intolerance is when the body does not make enough of an enzyme called lactase, which helps you digest lactose.
Lactose intolerance can start at any age and can also be caused by:
- conditions such as inflammatory bowel disease or coeliac disease
- bowel infections
- bowel surgery
- an injury to the bowel
Some premature babies are unable to digest lactose because their bowel has not developed enough, but this usually gets better as your baby gets older.
Some people do not make any lactase at all, but this is very rare.
