Lactose intolerance is a common digestive problem where the body is unable to digest lactose, a type of sugar mainly found in milk and dairy products.

Symptoms of lactose intolerance usually develop within a few hours of consuming food or drink that contains lactose. They may include:

flatulence (wind)

diarrhoea

bloated stomach

stomach cramps and pains

stomach rumbling

feeling sick

The severity of your symptoms and when they appear depends on the amount of lactose you’ve consumed.

Some people may still be able to drink a small glass of milk without triggering any symptoms, while others may not even be able to have milk in their tea or coffee.

When to seek medical advice

The symptoms of lactose intolerance can be similar to several other conditions, so it’s important to see your GP for a diagnosis before removing milk and dairy products from your diet.

For example, the symptoms above can also be caused by:

irritable bowel syndrome (IBS) – a long-term disorder that affects the digestive system

milk protein intolerance – an adverse reaction to the protein in milk from cows (not the same as a milk allergy)

If your GP thinks you have lactose intolerance, they may suggest avoiding foods and drinks containing lactose for two weeks to see if your symptoms improve.

Read more about diagnosing lactose intolerance.

What causes lactose intolerance?

The body digests lactose using a substance called lactase. This breaks down lactose into two sugars called glucose and galactose, which can be easily absorbed into the bloodstream.

People with lactose intolerance don’t produce enough lactase, so lactose stays in the digestive system where it’s fermented by bacteria. This leads to the production of various gases, which cause the symptoms associated with lactose intolerance.

Depending on the underlying reason why the body isn’t producing enough lactase, lactose intolerance may be temporary or permanent. Most cases that develop in adults are inherited and tend to be lifelong, but cases in young children are often caused by an infection in the digestive system and may only last for a few weeks.

Read more about the causes of lactose intolerance.

Who’s affected?

In the UK, lactose intolerance is more common in people of Asian or African-Caribbean descent.

Lactose intolerance can develop at any age. Many cases first develop in people aged 20 to 40, although babies and young children can also be affected.

Is it an allergy?

Lactose intolerance isn’t the same as a milk or dairy allergy. Food allergies are caused by your immune system reacting to a certain type of food. This causes symptoms such as a rash, wheezing and itching.

If you’re allergic to something, even a tiny particle can be enough to trigger a reaction, while most people with lactose intolerance can still consume small amounts of lactose without experiencing any problems (although this varies from person to person).

Treating lactose intolerance

There’s no cure for lactose intolerance, but limiting your intake of food and drink containing lactose usually helps to control the symptoms.

Depending on what dairy products you’re able to eat, you may also require additional calcium and vitamin D supplements to keep your bones strong and healthy. In some cases, your GP may refer you to a dietitian for further advice.

In addition to dietary changes, lactase substitutes may also be helpful. These are drops or tablets you can take with your meals or drinks to improve your digestion of lactose.

Read more about treating lactose intolerance.

Complications of lactose intolerance

Milk and other dairy products contain calcium, protein and vitamins such as A, B12 and D. Lactose also helps your body absorb a number of other minerals, such as magnesium and zinc. These vitamins and minerals are important for the development of strong, healthy bones.

If you’re lactose intolerant, getting the right amount of important vitamins and minerals can prove difficult. This may lead to unhealthy weight loss and put you at increased risk of developing the following conditions:

Osteopenia – where you have a very low bone-mineral density. If osteopenia is not treated, it can develop into osteoporosis.

Osteoporosis – where your bones become thin and weak. If you have osteoporosis, your risk of getting fractures and broken bones is increased.

Malnutrition – when the food you eat doesn’t give you the nutrients essential for a healthy functioning body. If you’re malnourished, wounds can take longer to heal and you may start to feel tired or depressed.

If you’re concerned that dietary restrictions are putting you at risk of complications, you may find it helpful to consult a dietitian. They can advise you on your diet and whether you require food supplements.