Lactose intolerance is one of the most common digestive conditions in the UK. It occurs when the body struggles to break down lactose — a natural sugar found in milk and dairy products. Lactose intolerance symptoms can range from mild discomfort to more noticeable digestive issues.
Understanding what causes it, how to recognise the signs, and what testing and dietary options are available can help you manage the condition effectively.
This guide covers the key symptoms of lactose intolerance, common causes, how to test for it, and practical advice on diet and treatment.
This article is for informational purposes only and does not replace medical advice. Individual experiences may vary.
What Is Lactose Intolerance?
What is lactose intolerance exactly? It is a digestive condition that occurs when the body does not produce enough of an enzyme called lactase. Lactase is responsible for breaking down lactose — the natural sugar found in milk and dairy products — into simpler sugars that the body can absorb.
When lactase levels are low, undigested lactose passes into the large intestine. There, bacteria ferment the lactose, producing gas and drawing water into the bowel. This is what causes the digestive symptoms associated with the condition.
It is important to note that lactose intolerance is not the same as a milk allergy. A milk allergy is an immune system response to proteins in milk and can cause more severe reactions, including skin symptoms and, in rare cases, anaphylaxis. Lactose intolerance is a digestive issue and does not involve the immune system.
Lactose intolerance is very common globally. Estimates suggest it affects a significant proportion of adults, with prevalence varying between ethnic groups and regions.
Lactose Intolerance Symptoms
The symptoms of lactose intolerance typically appear within 30 minutes to two hours after consuming dairy products. The severity depends on how much lactose has been consumed and how much lactase the body produces.
Common signs of lactose intolerance include:
Can lactose intolerance cause constipation? While diarrhoea is the more commonly reported symptom, some individuals may experience constipation. This can occur when undigested lactose affects gut motility. Symptoms vary between individuals and may depend on diet and other factors.
What Causes Lactose Intolerance?
Understanding what causes lactose intolerance can help clarify why symptoms develop. There are several recognised causes:
Reduced Lactase Production
The most common cause is a natural decline in lactase production after childhood. This is known as primary lactose intolerance. The body produces less lactase as it ages, which can gradually reduce the ability to digest dairy.
Age-Related Changes
Lactase levels often decline from early childhood onwards. Many people do not notice symptoms until adolescence or adulthood, when lactase production has decreased sufficiently to cause digestive discomfort.
Post-Infection Causes
A bout of gastroenteritis or another gut infection can temporarily damage the lining of the small intestine. This may reduce lactase production for a period, causing temporary lactose intolerance that often improves as the gut heals.
Secondary Intolerance
Conditions that cause gut inflammation — such as coeliac disease or Crohn's disease — can damage the intestinal lining and reduce lactase production. This is known as secondary lactose intolerance and may improve if the underlying condition is managed.
Genetic Factors
Genetics play a significant role. Lactose intolerance is more prevalent in people of East Asian, African, South Asian, and Middle Eastern descent. In contrast, populations with a long history of dairy farming tend to retain higher lactase levels into adulthood.
Can You Develop Lactose Intolerance Later in Life?
Can you develop lactose intolerance as an adult? Yes. It is quite common for adults to notice digestive symptoms developing gradually over time. This often leads people to ask: why am I suddenly lactose intolerant?
In most cases, the change is not truly sudden. Lactase production declines gradually, and the tipping point — where symptoms become noticeable — may seem to arrive unexpectedly. However, the reduction has likely been progressing over years.
Some adults develop symptoms after a gut infection, surgery, or a period of reduced dairy intake. In these cases, the onset may feel more abrupt.
Does lactose intolerance go away? Primary lactose intolerance, caused by a natural decline in lactase production, does not typically resolve. However, secondary lactose intolerance — caused by gut inflammation or infection — may improve once the underlying condition is addressed. Individual experiences vary.
Lactose Intolerance in Infants
Lactose intolerance in infants is less common than in adults but can occur. There are two main forms to be aware of:
Important: If you have concerns about your infant's digestion or suspect lactose intolerance, consult your GP or paediatrician. Appropriate assessment is essential before making any changes to an infant's diet.
Wondering If You May Be Lactose Intolerant?
Diagnostic testing may help identify whether your symptoms are linked to lactose malabsorption.
How to Test for Lactose Intolerance
If you find yourself asking “am I lactose intolerant?”, a lactose intolerance test may help provide clarity. There are several approaches to testing, each with its own method and purpose.
Hydrogen Breath Test
This is one of the most commonly used methods. After consuming a measured dose of lactose, the patient breathes into a device at regular intervals. Elevated hydrogen levels in the breath may indicate that lactose is not being properly digested.
Blood Glucose Testing
A blood sample is taken before and after consuming lactose. If blood glucose levels do not rise as expected, it may suggest that lactose is not being broken down and absorbed properly.
Elimination Diet
This involves removing all dairy products from the diet for a period — typically two to four weeks — and monitoring whether symptoms improve. Dairy is then gradually reintroduced to assess tolerance levels. This approach is best carried out under professional guidance.
Laboratory Diagnostic Testing
Private blood testing may form part of a broader investigation into digestive symptoms. Laboratory analysis can help identify markers that support a clinical picture of lactose malabsorption.
Please note: All testing is subject to suitability and clinical assessment. Results represent a clinical snapshot at the time of testing.
Lactose Intolerance Treatment Options
Lactose intolerance treatment focuses on managing symptoms and adjusting dairy intake to a comfortable level. There is no cure, but the condition can be managed effectively in most cases.
These approaches may help reduce symptoms, but individual responses vary. For persistent or severe symptoms, professional guidance from a dietitian or healthcare provider is recommended.
Lactose Intolerance Diet
A well-planned lactose intolerance diet can help manage symptoms while maintaining adequate nutrition. Understanding which foods contain high levels of lactose — and which are lower or lactose-free — is key.
Lactose Intolerance Foods to Avoid or Limit
| Category | Examples |
|---|---|
| High-lactose foods | Cow's milk, soft cheeses (ricotta, cottage cheese), ice cream, cream, condensed milk |
| Lower-lactose options | Hard cheeses (cheddar, Parmesan), butter, natural yoghurt, fermented dairy |
| Lactose-free alternatives | Lactose-free milk, oat milk, soya milk, almond milk, coconut yoghurt |
Key dietary considerations:
When to Consider Testing
You may wish to consider a lactose intolerance test if you experience:
If you would like further information about diagnostic testing options, you may explore our medical services or contact our clinic team.
Summary
Lactose intolerance is a common and manageable digestive condition. The key symptoms — bloating, abdominal discomfort, gas, and diarrhoea — typically develop after consuming dairy products and vary in severity between individuals.
The causes range from a natural age-related decline in lactase production to secondary factors such as gut infections or inflammatory conditions. Many people develop symptoms gradually over time, while others notice a more sudden change.
Testing options — including breath tests, blood glucose tests, and elimination diets — can help confirm the condition. Treatment focuses on dietary adjustments, lactase supplements, and monitoring individual tolerance levels.
With the right approach, most people with lactose intolerance are able to manage their symptoms effectively and maintain a varied, nutritious diet.
Frequently Asked Questions
What are the main symptoms of lactose intolerance?
Common lactose intolerance symptoms include bloating, abdominal discomfort, gas, diarrhoea, and nausea. Symptoms typically appear within 30 minutes to two hours after consuming dairy products. The severity varies between individuals and depends on how much lactose has been consumed.
Can you develop lactose intolerance later in life?
Yes. Lactose intolerance can develop at any age. It is common for lactase production to gradually decrease after childhood, meaning some adults may notice symptoms developing over time. This is known as primary lactose intolerance and is the most common form.
How do you test for lactose intolerance?
A lactose intolerance test may include a hydrogen breath test, a blood glucose test, or a supervised elimination diet. Laboratory diagnostic testing can help identify whether symptoms are linked to lactose malabsorption. Results represent a clinical snapshot at the time of testing.
What is the difference between lactose intolerance and a milk allergy?
Lactose intolerance is a digestive condition caused by a lack of the enzyme lactase. A milk allergy is an immune system response to proteins found in milk. Milk allergy can cause more severe reactions, including skin symptoms and, in rare cases, anaphylaxis. The two conditions require different approaches to management.
Can lactose intolerance cause constipation?
While diarrhoea is the more commonly reported symptom, some individuals with lactose intolerance may experience constipation. This can occur when undigested lactose affects gut motility. Symptoms vary between individuals and may depend on diet and other factors.
Does lactose intolerance go away?
Primary lactose intolerance, which is caused by a natural decline in lactase production, does not typically resolve. However, secondary lactose intolerance — caused by gut inflammation or infection — may improve once the underlying condition is addressed. Individual experiences vary.
What foods should you avoid with lactose intolerance?
High-lactose foods include milk, soft cheeses, ice cream, cream, and yoghurt. Many people with lactose intolerance find they can tolerate small amounts of dairy or certain lower-lactose options such as hard cheeses, butter, and fermented dairy products. Lactose-free alternatives are also widely available.
Considering Diagnostic Testing?
If you would like further information about diagnostic testing options, our clinic team is available to help. All testing is subject to suitability and clinical assessment.