Lactose Intolerance - Causes, Symptoms & Treatment

Lactose intolerance is when you experience symptoms like diarrhoea, stomach pains or bloating, after eating foods that contain lactose. Lactose intolerance symptoms can start minutes or hours after having products with lactose. 

If you are lactose intolerant, it means your body isn’t producing enough of the enzyme called lactase. 

Lactose intolerance is common in adults, and it can’t be prevented. What causes lactose intolerance varies in each person. Thankfully, there are things you can do to relieve the symptoms!


Lactose intolerance can give you unpleasant symptoms. The symptoms of lactose intolerance can vary from mild to severe. The severity of the symptoms can depend on how much lactose you have had or your tolerance. 

Lactose intolerance symptoms can present quickly after a food or drink with lactose has been consumed, or they might take up to two days to show. 

Symptoms of lactose intolerance include:

Lactose intolerance is different to a food allergy. An allergy to products such as milk can cause anaphylaxis which is considered to be a medical emergency. 


There are three different types of lactose intolerance, all with different causes.

Primary lactose intolerance

Primary lactose intolerance is the most common type. People who develop primary lactose intolerance produce enough lactase in their early life. Babies get all of their nutrition from drinking milk and need lactase. 

As baby’s grow into children they start to replace milk with other foods and the amount of lactase they produce decreases. The lactase produced usually remains high enough to digest the amount of dairy in a typical adult diet. 

However, by the time adulthood arrives lactase production decreases drastically. Milk products become more difficult to digest, leading to the development of primary lactose intolerance. 

Secondary lactose intolerance

Secondary lactose intolerance usually happens after an illness or surgery that involves your small intestine.

Crohn's disease, bacterial overgrowth, celiac disease and intestinal infection are all associated with secondary lactose intolerance. In some cases, treating an underlying disorder can restore lactase levels.

Congenital or developmental lactose intolerance

Congenital or developmental lactose intolerance refers to babies born with lactose intolerance due to a lack of lactase. It is passed down, with both parents passing the same gene variant to the baby. Premature babies can also be lactose intolerant due to a poor lactase level. 


Lactose is found in dairy products. It includes, but is not limited to, milk from cows, sheep and goats. Dairy products include:

  • Milk 
  • Cheese 
  • Cream 
  • Yoghurt 
  • Butter 
  • Ice cream 

A lot of processed foods might also contain lactose and can include:

  • Baked foods (e.g. bread, crackers, cakes, biscuits and pastries)
  • Sauces and salad dressings
  • Cereals 
  • Diet and protein shakes 

If you are worried about what foods contain lactose you can find more information here

If you’re lactose intolerant, you also need to make sure you are checking the patient information leaflet of any medication or with your prescriber to avoid a flare-up. 


If you have symptoms of lactose intolerance you should visit your GP to rule out any other issues and confirm the diagnosis. Before you visit your GP be sure to make note of your symptoms, and if possible, keep a food diary.

If your GP thinks you are lactose intolerant they will ask you to follow a lactose elimination diet. You will be required to stop eating foods containing lactase to see if your symptoms improve.

Your GP can confirm the diagnosis with tests. The first test they might carry out is the hydrogen breath test. 

After drinking a liquid with high levels of lactose, your doctor will measure the amount of hydrogen in your breath at regular intervals. Having too much hydrogen in your breath suggests that you aren’t fully digesting and absorbing lactose. 

A lactose tolerance test might also be carried out. You will be required to drink a liquid containing high levels of lactose. 

Two hours after you have had the liquid, blood tests will be carried out. The blood tests will measure the amount of glucose in your bloodstream. If your glucose level doesn’t rise then your body has not properly digested and absorbed the drink.

If you experience any of the following, you could be having a severe allergic reaction and you should visit A&E immediately:

  • Difficulty breathing or talking 
  • Wheezing 
  • Tightness in your chest or your throat 
  • Swelling in your mouth, face, lips, tongue or throat
  • A rash
  • Itchy, red, swollen, blistered, peeling skin


Watch dairy products 

Many people with can enjoy some milk products without suffering the consequences. You might be able to tolerate low-fat milk products like semi-skimmed milk over full fat. 

It is also possible to increase your tolerance to dairy produce by slowly introducing them into your diet. 

When you choose to drink milk, opt for smaller servings each time. The smaller the serving, the less chance of suffering from lactose-induced symptoms. 

You should save your milk for meal times. Having milk with other food slows the digestive process down. 

Not all dairy products contain the same amount of lactose. Hard cheeses have a small amount of lactose and typically cause no symptoms. 

Ice cream and milk have the highest amount of lactose, however, the high-fat content in these products may allow you to tolerate them with zero symptoms. 

Lactose-reduced and lactose-free products

Most supermarkets will stock a range of lactose-free products. They are usually found close to the dairy section. By substituting dairy products for lactose-free products you can still enjoy substitutes of your favourite foods.

Lactose enzyme tablets or drops

Over-the-counter (OTC) tablets and drops are available to purchase. They contain the lactase enzyme which can help assist with the digestion of dairy products. The tablets can be taken before a meal or snack and even added to milk. 

You can lead a normal life with lactose intolerance and it is more common in people in the UK than you might think!

If you find you are struggling with restrictions of your diet or believe that you are at risk of complications or ill health then make sure you speak to your GP.

You can also contact a private dietitian if you need further support. 

Olivia Malone - Medical Content Writer
James O'Loan - CEO & Superintendent Pharmacist
James O'Loan , CEO & Superintendent Pharmacist on 03 July 2023
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