Your Complete Guide to Lactose Intolerance: Causes, Symptoms, Diagnosis and Treatment

February 20, 2023 10 min read

Your Complete Guide to Lactose Intolerance: Causes, Symptoms, Diagnosis and Treatment

Your Complete Guide to Lactose Intolerance: Causes, Symptoms, Diagnosis and Treatment


Lactose intolerance is a common issue that usually manifests in symptoms such as tummy pain, bloating and gas, shortly after eating foods that contain lactose. Some people experience more severe symptoms like feeling or being sick, too. 

Lactose is a type of sugar found in milk and dairy products. If you can’t digest lactose properly, it can lead to some uncomfortable side effects soon after eating milk-based foods. 

Layer Origin’s human milk oligosaccharides (HMOs) are fermented from lactose, and we are often asked if you can take our HMO products if you’re lactose intolerant. We aim to answer that question and give you a detailed overview of what intolerance is in this article. 

What is lactose? 

Lactose is a type of sugar found in animal milk. It’s not just found in cow’s milk but also goats and sheep. The namelactose comes from the Latin word for milk,lac, and the suffix -ose which is used to name and define sugars. 

Lactose is a disaccharide which means there are two monosaccharide sugars joined together by a glycosidic linkage. In the case of lactose, the two sugars are glucose and galactose. When you eat foods containing lactose, your body produces an enzyme called lactase to break it down and allow absorption. 

What is lactose intolerance?

Lactose intolerance is a condition that occurs in people who are unable to digest or absorb lactose properly. It is caused by your body not producing enough lactase to break down lactose into its two sugars, glucose and galactose.

Because the enzyme is not present to break it down, lactose remains in the digestive system and is fermented by bacteria instead. It’s this fermentation that results in the symptoms associated with lactose intolerance and the production of excess gas

Symptoms of lactose intolerance

The symptoms of lactose intolerance usually occur within two hours of ingesting lactose and include:

  • gas (wind)
  • bloating
  • diarrhoea
  • stomach pain and cramps
  • rumbling tummy
  • feeling or being sick

Some people find that the more lactose they consume, the more severe their symptoms are. And the severity of intolerance can vary from person to person. For example, some individuals may be able to drink a small glass of milk while others won’t even be able to have a small amount of milk in their morning coffee. 

Causes of lactose intolerance

The usual cause of intolerance is your body not producing enough lactase to break down and digest lactose. Without enough lactase, the lactose moves through your body into your gut where it is fermented by your gut bacteria, resulting in unpleasant digestive symptoms.

But lactose intolerance can affect anyone, at any age because there are several types.

Primary lactose intolerance

Primary lactose intolerance occurs because of a genetically programmed reduction in lactase production shortly after weaning. So, babies produce lactase normally but as they age their production of this enzyme decreases until they are no longer able to absorb lactose.

It is estimated that up to 66% of the world’s population is affected by primary lactose intolerance, making it the most common form. 

Secondary lactose intolerance

Secondary lactose intolerance occurs because of another condition that affects lactase production in the small intestine. Some causes of secondary lactose intolerance include:

  • coeliac disease
  • Crohn’s disease
  • ulcerative colitis 
  • abdominal surgery
  • gastrointestinal infection

Secondary lactose intolerance which is not caused by a long-term condition is often temporary and can be treated by removing lactose from your diet for eight weeks, giving the gut enough time to heal.

Congenital lactase deficiency

Congenital lactase deficiency, also known as alactasia, is an inherited but rare form of lactose intolerance. Newborns whose parents both have the same genetic mutation for this type of lactose intolerance are born with the condition. 

Babies born with congenital lactose intolerance usually present with severe watery diarrhoea shortly after beginning breastfeeding. These individuals have a normal small intestinal mucosal lining but no lactase production. Most cases of congenital lactose intolerance are reported in Finland and Western Russia.

Developmental lactase deficiency

Developmental lactose intolerance occurs in babies, usually, those who are premature and born before their digestive system has fully developed, causing digestive stress symptoms.

The condition is often temporary and should resolve as the baby develops. Babies are likely to go on to consume foods containing lactose. However, in the meantime, they’ll need lactose-free formula milk.

Lactose intolerance risk factors

The risk of developing lactose intolerance may be higher in certain individuals. For example, anyone who:

  • is of African or Asian heritage
  • has a history of digestive problems or disease
  • has a family history of lactose intolerance

Can you develop lactose intolerance over time?

Yes, lactose intolerance can affect anyone at any age. Some people will be able to tolerate lactose for their whole lives whereas others will become less tolerant as they age. It can also be caused by other conditions affecting the gut such as inflammatory bowel disease (IBD). 

As you age, your body naturally starts to produce less lactase which can also contribute to the development of lactose intolerance. 

Can I eat dairy foods if I’m lactose intolerant?

Lactose intolerance is different to an allergy. For example, a milk or dairy allergy is caused by your immune system reacting to milk or dairy-based food and can cause symptoms like wheezing, skin rash, and itching. An allergy means even a tiny particle of what you are allergic to is enough to spark a reaction. However, people who are lactose intolerant are often able to eat a small amount of lactose before experiencing symptoms. But this can vary from person to person. 

If you are lactose intolerant, it’s likely you are already aware of how much lactose your body can tolerate before you experience unpleasant side effects. If this amount is tiny, it’s likely to be advisable to avoid lactose altogether. 

Many supermarkets and health food shops now stock lactose-free dairy products, so you may still be able to consume your favourite milk-based food and drinks. If not, there are oat, coconut and soya-based alternatives available. 

Foods that contain lactose

Lactose is found in foods containing animal milk, including cows, goats and sheep. Lactose-containing foods include:

  • milk
  • butter
  • cheese
  • yoghurt
  • cream
  • ice cream
  • sauces
  • salad dressings
  • cereals
  • baked foods
  • milk and protein shakes

If you are concerned about the lactose content of any food or drink, check the label.

How is lactose intolerance diagnosed? 

If you think you may be lactose intolerant, you should speak to your doctor because it can share symptoms with other digestive conditions. 

To help with the diagnosis, it can help to keep a food diary detailing what you eat and drink as well as the symptoms you experience after eating. 

You may be advised to remove lactose from your diet for two weeks to see if this helps to alleviate the symptoms. If it does, this can provide further evidence for lactose intolerance.

Hydrogen breath test

A hydrogen breath test may also be used to test for lactose malabsorption. This type of test can be used for several conditions and is considered the gold standard for diagnosing small intestinal bacterial overgrowth (SIBO)

The test measures the amount of hydrogen present in your breath after ingesting lactose. High levels of hydrogen may be indicative of lactose intolerance. A lactose hydrogen breath test is more sensitive than a lactose tolerance test.

Lactose tolerance test

During a lactose tolerance test, you’ll be given a drink of lactose solution and a small blood sample will be taken from a vein in your arm. The blood sample will be tested to determine how much sugar (glucose) is in your blood after consuming lactose.

If your body can’t tolerate lactose, then your blood sugar levels are likely to rise slowly or not at all, because it is unable to break down lactose into its two constituent sugars, glucose and galactose. 

How to treat lactose intolerance

In most cases, lactose intolerance can be managed by making some simple changes to your diet and lifestyle. For example, many people with lactose intolerance choose to avoid foods that contain the sugar, while others may just limit the amount of lactose they consume in a day

Lactase products

Some people benefit from lactase supplementation. Ingested lactase is easily ingested and broken down by stomach acid, so can help to lessen or relieve the symptoms of lactose intolerance in some individuals.

Treating underlying conditions

If your lactose intolerance is caused by an underlying condition such as inflammatory bowel disease or coeliac disease, treating these may help manage the symptoms of lactose intolerance.

Probiotic and prebiotic use

Some research has shown that both probiotics, live microorganisms that when taken in large enough quantities can induce health benefits, and prebiotics, nourishment for probiotics, may help to reduce lactose intolerance symptoms.

A systematic review published in 2018, revealed that there was a positive relationship between the use of probiotics and lactose intolerance. Furthermore, probiotics, especially yoghurt bacteria, which contain high levels of lactase have been shown to ease lactose intolerance.

Specific prebiotics such as galacto-oligosaccharides (GOS) have also been shown to modulate the gut microbiome, promote the growth and activity of good gut microbes, and reduce the symptoms of lactose intolerance.

Overall, modulating the human gut microbiome and increasing lactose-fermenting species, particularly Bifidobacteria and Lactobacillus may help to alleviate lactose intolerance in some people. 

Do human breast milk and HMOs contain lactose?

Within human breast milk, there are numerous biomolecules, including lactose, fats (lipids), and of course, human milk oligosaccharides (HMOs). You may be surprised to find that human breast milk contains more lactose than cow’s milk. Approximately 100 ml of human breast milk contains 7.5g of lactose compared to 5g per 100 ml of cow’s milk

Lactose is the main carbohydrate present in breast milk and almost all HMOs contain lactose at their core. Lactose can be fucosylated, having fucose sugar units added to it, or sialylated, reacted with sialic acid, to produce the small HMOs you may be familiar with, such as:

  • 2’-fucosyllactose (2’-FL)
  • 3’-fucosyllactose (3’-FL)
  • 3’-sialyllactose (3’-SL)
  • 6’-sialyllactose (6’-SL) 

What are Layer Origin’s HMOs?

Human milk oligosaccharides are naturally present in human breast milk. The HMO supplements we provide are considerednext-generation because they are fermented from high-purity lactose present in cow’s milk.  So, PureHMO® products do not contain any human milk but the HMOs are bioidentical to those found in breast milk.

Technically, Layer Origin HMOs are referred to as Human identical Milk Oligosaccharides or HiMO for short. 

I am lactose intolerant, can I take PureHMO® products?

The simple answer to this is yes. Layer Origin’s HMOs are derived from the lactose present in cow’s milk which means they do contain lactose. However, research has shown that people who are lactose intolerant can usually take:

  • up to 12g or 250 ml of milk in one go
  • up to 24g or 500 ml of milk spread across the day

The recommended serving size of our HMOs is 2g which means lactose-intolerant individuals should be able to take the powder or capsules without experiencing any side effects. 

If you are unsure, try taking a low dose and build up to the recommended daily dose to see how your body reacts to the HMOs. 

Can I take HMOs if I have a milk allergy?

Milk proteins are responsible for causing an allergic reaction to milk. Although Layer Origin’s HMO products contain no detectable milk proteins, it is recommended that you seek advice from your physician before taking HMOs. 

Why take HMOs?

If you’re not already a converted HMO-er, then here are a fewreasons to help convince you to invest in your 1st pot and your gut health: 

  • increase the abundance and activity of Bifidobacteria and Akkermansia
  • HMOs support immune function
  • HMOs could improve cognition
  • they may offer protection against chronic disease 
  • HMOs may help with weight loss by increasing the abundance of Bifidobacteria, a bacteria species often found in lean individuals 

You can explore our range of gut-boosting productshere.


Lactose intolerance is a collection of symptoms that occur shortly after ingesting foods containing a specific type of sugar called lactose. Lactose intolerance occurs because your body is deficient in lactase, the enzyme responsible for breaking down lactose.

The symptoms can be unpleasant and may include diarrhoea, bloating, and excess gas. Lots of people are lactose intolerant and can manage the condition by making small changes to their diet and lifestyle.

Because many people with the condition can tolerate small amounts of lactose, Layer Origin’s PureHMO® products are safe for you to take.


Written by: Leanne Edermaniger, M.Sc. Leanne is a professional science writer who specializes in human health and enjoys writing about all things related to the gut microbiome. 



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