Real Talk about:

Are all Humans Lactose Intolerant?

Lactose Intolerance and Dairy Allergy Explained

Food hypersensitivity is the appropriate medical term used to describe any adverse reaction to a particular food. Cow’s milk protein allergy and lactose intolerance are the two main hypersensitivities relating to dairy. Although they are often confused, they are two very distinct conditions. Also, dairy hypersensitivities are not the same as gluten intolerance or gluten allergy (coeliac disease) and each condition requires expert diagnosis by a registered clinician, in order to avoid unnecessary or inappropriate changes to the diet. This article will examine lactose intolerance and milk allergy, with a focus on the signs and symptoms, how common they are and whether they can be cured.

What is milk allergy?

Milk allergy, like all allergies, is the immune system’s abnormal reaction to a protein, in this case a milk protein.  Food allergies are most common in infancy due to the immaturity of the new-born digestive and immune systems. In Ireland, about 2-3% of infants have a cow’s milk allergy. For these infants, absolute exclusion of dairy products is necessary initially but up to 90% of children outgrow the allergy by the age of 3-5 years. Therefore, cow’s milk allergy is uncommon among adults.

What is lactose intolerance?

Most people with lactose intolerance have ‘primary lactose intolerance’, which occurs in adults who have low levels of the enzyme needed to digest the naturally occurring sugar in milk, known as lactose. Lactose is usually broken down by lactase and absorbed in the small intestine, along with calcium and other nutrients. Undigested lactose can cause problems within the digestive system with a build-up of excess gas and fermentation products in the large intestine.

Transient or secondary lactose intolerance can be a consequence of illness such as food poisoning and in such cases usually subsides within a few weeks. This acute lactose intolerance can also be associated with chronic conditions such as Irritable Bowel Disease and Coeliac Disease, where lactase production is inadequate due to the damaged intestine surface.

Congenital lactose intolerance is a rare but severe condition. It presents in the neonatal period in infants that have a complete absence of lactase production. These infants usually need specific care and even a small amount of lactose is not tolerated.

Worldwide, it is estimated that about 65% of people carry the gene which results in reduced lactase production after weaning, but it varies largely across populations, ranging from 4% to over 80% across different parts of the world. Due to genetic evolution, Ireland has a lower prevalence of lactose intolerance, with 4-5% affected.

What is the difference between dairy allergy and intolerance?

  Cow’s Milk Protein Allergy Lactose Intolerance
Common Symptoms Symptoms are usually immediate (less than 2 hours) or delayed, depending on the allergy type.


– Gastrointestinal e.g. vomiting, diarrhoea              – Dermatological e.g. hives, rash

– Respiratory e.g. wheezing


If the reaction is severe, breathing problems can occur where the throat may swell up or close. This is an ‘anaphylactic’ reaction and requires immediate medical assistance

Lactose intolerance symptoms are not life threatening and may start to appear 30 minutes to 2 hours after eating lactose-containing foods:

Mainly gastrointestinal e.g. upset stomach, trapped wind, diarrhoea, cramps, bloating.


Caution Symptoms can often be confused with those of other medical conditions and accurate diagnosis is essential. Take care as some non-medical tests have no scientific basis or proven role (e.g. hair analysis, isolated IgG testing, kinesiology, vega-testing, enzyme potential desensitisation).


Cutting out dairy could lead to nutritional inadequacies, so consultation with a registered dietitian is advised. Dairy foods are a source of calcium and several other nutrients.

Diagnosis A focused clinical history combined with skin prick test and/or blood test for specific ‘IgE antibodies’ is most common. Elimination and reintroduction testing should be performed under medical supervision. Your practitioner will carry out a specific lactose intolerance test which involves elimination and reintroduction testing. A hydrogen breath test may also be performed to detect undigested lactose.
Prevalence in Ireland 2-3% (mainly infants, with up to 90% growing out of it by age 3-5 years) 4-5% in Ireland (varies in different parts of the world and by ethnicity)
Management Exclusion of dairy foods through a dairy-free diet for as long as the allergy persists.


Other mammalian milks such as goat and sheep are generally not suitable replacements as some may cause similar reactions. Plant-based (dairy free) alternatives are not nutritionally comparable to cow’s milk, so other foods should also be included to meet the nutritional shortfall.


Food challenge tests for safe re-introduction are performed under the supervision of a registered clinical expert, such as a dietitian. The dietitian uses a stepwise approach, called a ‘milk ladder’ to safely re-introduce dairy products until the allergy subsides. Re-introduction usually begins with baked milk products.

Depending on tolerance level, most people can consume some lactose, which can be preferable than absolute exclusion. The majority with lactose maldigestion (problems digesting lactose) will tolerate up to 12 g as a single dose with no or minor symptoms (see diagram below).


There are a number of lactose-free products available commercially, such as lactose-free milk.


Lactase supplements (the enzyme that digests lactose) are also available from pharmacies and health stores which can assist with lactose digestion, when taken at the correct time.


Does lactose intolerance mean you have to cut out dairy?

No, in most cases, dairy foods do not need to be completely avoided but need to be limited to the person’s individual tolerance. Tolerance levels vary, with some individuals only having symptoms of lactose intolerance or digestive discomfort following the consumption of large amounts. Consumption of some lactose can promote tolerance in these individuals. According to the European Food Safety Authority, typically, up to 12g at a time can be consumed with no, or minor, symptoms. Some dairy foods have negligible amounts of lactose:

Lactose intolerance

Lactose – not the same as normal sugar!

Milk contains a naturally occurring type of sugar, lactose (approximately 5 g per 100 ml). Like all sugars, lactose belongs to the carbohydrate family. Generally, sugar is not added to milk unless specified in the ingredients list e.g. in flavoured milks. The World Health Organisation (WHO) have focused on restricting ‘added’ or ‘free’ sugars plus sugars naturally present in honey, syrups and unsweetened fruit juices. It is important to remember that lactose does not fall into this category of ‘added’ or ‘free’ sugars, even though it is still declared as ‘sugar’ on nutrition labels.

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