18. November 2019
Intestinal bacteria and cow’s milk allergy

One in 200 children under the age of two in Europe has a cow’s milk allergy. The microorganisms in the gut may be a factor. An article summarising the available evidence and remaining questions was published in mid 2019.

What did the researchers do?

They reviewed studies from the last several years on cow’s milk allergy and the role of beneficial gut bacteria (microbiome) and summarised the key findings. They looked specifically at pre-, pro- and synbiotics.

The review was conducted by an international research team headed by London-based paediatric allergy specialist Adam Fox.


What are pre-, pro and synbiotics?

  • Prebiotics are non-digestible food ingredients that promote the growth of bacteria in the large intestine. These include certain polysaccharides such as inulin, but also sugar derivatives such as lactulose from milk sugar (lactose).
  • Probiotics are live microorganisms that are naturally present in the healthy gastrointestinal tract. These include lactic acid bacteria and yeasts, for example.
  • Synbiotics are a combination of the two.


How prevalent is cow’s milk allergy?

Cow’s milk allergy can occur in up to five percent of all infants in some countries. A large study of over 12,000 infants in nine European countries (Schoemaker 2015) revealed that cow’s milk allergies are not as common in Europe. Around 0.5 per cent of all children up to two years of age are affected. The figure is around 1.3 per cent in the UK and Northern Ireland, and even less than 0.3 per cent in Germany, or less than three in 1,000 children. 


What were the results?

  • There have previously only been a few studies comparing the microbiomes of healthy children and children with allergies.
    Children with allergies appeared to have fewer bifidobacteria and lactic acid bacteria in the gut. However, this particular study dates back nearly 20 years old (Kirjavainen 2002).
  • The EAACI (European Academy of Allergy and Clinical Immunology) suggests that infants who are not exclusively breastfed be given prebiotics to prevent allergies.
  • Previous studies provide no evidence that probiotics reduce allergies in children. Nevertheless, the World Allergy Organization (WAO) Guidelines Committee assumes that probiotics are beneficial to children because they prevent skin rash (eczema).
  • The WAO therefore recommends probiotics to prevent food allergies in children at high risk of allergies. They are also recommended for pregnant women and nursing mothers whose children are at high risk of allergies. However, the committee cautions that the quality of the studies on this subject is poor. It also remains unclear which probiotics should be used and when. Overall, very different results were obtained from the probiotic studies, which could be due to the fact that they involved different strains of bacteria.
  • With regard to synbiotics, the authors mention a study investigating infants with atopic dermatitis (Van der Aa 2010): The children were given extensively hydrolysed formula (EHF), which is formula containing cow’s milk proteins that have been broken down (hydrolysed) so that the body no longer recognises them as a foreign substance. One group received the EHF with synbiotics, the other group without. In children with IgE-mediated atopic dermatitis, the dermatitis symptoms were significantly milder if they had received the synbiotics.


Why is the study important?

The review article shows how little research has been done on the effects of the microbiome on allergies.


No one knows exactly how the microbiome in people with cow’s milk allergy compares to a healthy microbiome. What is normal and what causes disease?


There are not enough methods available that allow the microbiome to be correctly understood. We also don’t know exactly which bacterium should be present in the gut during childhood development and how changes in the microbiome progress. Furthermore, there are no methods for rapid diagnosis in hospital.


Which pre-, pro or symbiotic treatment should be given and in which quantities? And if the microbiome changes, what effect does it have precisely on the prevention or treatment of cow’s milk allergy? These questions remain unanswered. The guideline committees therefore agree that further research is needed.


But one of authors’ recommendations can be implemented immediately: Primary care physicians, or general physician and doctors in emergency outpatient departments, should be better informed about cow’s milk allergy. The non-IgE mediated allergy in particular is frequently overlooked.


Original study

Fox A et al. The potential for pre-, pro- and synbiotics in the management of infants at risk of cow’s milk allergy or with cow’s milk allergy: An exploration of the rationale, available evidence and remaining questions. World Allergy Organ J. 2019;12(5):100034.


Additional sources

Fiocchi A et al. Incremental prognostic factors associated with cow’s milk allergy outcomes in infant and child referrals: the Milan Cow’s Milk Allergy Cohort study. Ann Allergy Asthma Immunol 2008;101:166-73.


Fiocchi A et al. World Allergy Organization-McMaster University Guidelines for Allergic Disease Prevention (GLAD-P): Probiotics. World Allergy Organ J. 2015 Jan 27;8(1):4.


Kirjavainen PV, et al. Aberrant composition of gut microbiota of allergic infants: a target of bifidobacterial therapy at weaning? Gut. 2002 Jul;51(1):51-5.


Koike Y et al. Predictors of Persistent Milk Allergy in Children: A Retrospective Cohort Study. Int Arch Allergy Immunol. 2018;175(3):177-80.


Schoemaker AA et al. Incidence and natural history of challenge-proven cow’s milk allergy in European children – EuroPrevall birth cohort. Allergy 2015;70(8):963-72.


Van der Aa LB et al. Effect of a new synbiotic mixture on atopic dermatitis in infants: a randomized-controlled trial. Clin Exp Allergy. 2010;40:795– 804.