The rise in allergies among young and old, alike, has not escaped the notice of both practitioner and layperson. Allergic diseases affect over 30 percent of individuals in many communities, but it is also estimated that the prevalence of allergic diseases in infants is approximately 30 percent in those with an allergic first-degree relative. Some blame the increase in toxin exposure and others blame the food, but most everyone admits the answers are not clear. Whether it be food, environmental, or skin allergies, one common denominator is the immune system and especially, its inflammatory department. But we can’t stop there. The immune system is very intricately linked to the microbiome of the entire body -  not just that which resides in the gastrointestinal tract. In fact, it has often been said that the health and function of the immune system are directly associated with the diversity and health of the microbiome. If this is the case, then it is reasonable to consider the microbiome when seeking to solve the allergy enigma.

Most allergic reactions are manifested in the gastrointestinal tract, respiratory tract, and/or skin. Not surprisingly, these organ systems are also where the body’s microbiome is most heavily concentrated. A variety of bacterial species make their home in the intestinal tract, the mucous membranes, and on the surface of the epidermis. Considering that these three organ systems also represent the primary portals of entry for pathogens, it again is logical to see that the microbiome is so heavily concentrated here as it functions as the first line of defense against invading pathogens and antigens. A weak microbiome, or one which lacks biodiversity, is a poor defense system and therefore, the immune system is required to “pick up the slack” in identifying and protecting the body against invaders, which includes common allergens.

Several researchers have questioned the role of the microbiome in regulating the response of the immune system to potential antigens and eliciting an allergic response. For example, it has been found that an altered innate and adaptive immune response is responsible for allergic dermatitis (AD) and that skin inflammation is exacerbated by microbial dysbiosis in those with AD. Further, when the skin is colonized with Staphylococcus aureus, there is an increased IgE response, IL-4 and IL-13 expression, and increased food allergies. Likewise, children with milk allergies have higher total bacteria and anaerobic counts in their intestinal microbiome and children with peanut allergies had reduced microbial richness compared to healthy controls. However, when the microbiome of children with food allergies was enriched with Firmicutes such as Clostridia, their allergies resolved. Animal studies showed that Clostridia could modulate the allergic response of the immune system by reducing total IgE and improving epithelial integrity, repair, and homeostasis through the production of short-chain fatty acids.

As researchers link a healthy microbiome to the function of the immune system in allergic conditions, more attention is being given to the role of prebiotics and probiotics in preventing and managing allergic conditions. In a systematic review and meta-analysis of randomized controlled trials seeking to evaluate the effect of early prebiotic supplementation on the risk of developing allergies, it was found that prebiotic supplementation during infancy reduced the risk of eczema, asthma, and food allergy. In fact, the risk for food allergies was reduced from 170 per 1000 children to 48 per 1000 children with prebiotic supplementation. Eczema is a common allergic manifestation of a cow’s milk allergy in children.

Another study, the worldwide, multicentre PATCH trial (Primary Allergy Prevention Through Cow's Milk Hydrolysates), included 1047 infants at risk for a cow’s milk allergy and found that the microbiome of infants fed a partially hydrolyzed protein formula supplemented with prebiotic oligosaccharides for six months more closely matched that of a breastfed infant, compared to infants fed a cow's milk formula. The result was a reduced risk of cow’s milk allergy among those infants at risk due to having a parent with a reported allergy. The European Academy of Allergy and Clinical Immunology (EAACI) now recommends using prebiotic supplementation for the prevention of allergy in not-exclusively breastfed infants regardless of their allergic risk to reduce the risk of allergy. Additionally, the World Allergy Organization (WAO) recommends using prebiotic supplementation only in infants not-exclusively breastfed to prevent the risk of allergy.

Prebiotics are not only just a food source for microbial strains, supporting their survival and colonization but also a unique food source that is fermented into short-chain fatty acids (SCFA) which play a role in immune development and maturation during early life, promote gut homeostasis and the regulation of inflammatory responses, epithelial integrity, IgA antibody responses, and can even epigenetically modify DNA.

In light of the devastating effects of allergic diseases, prebiotic supplementation in early infancy and childhood seems like a small price to pay for the high reward of preventing the development of these allergic reactions. And for those that are older, prebiotic supplementation can still support the microbiome, strengthen the immune system, and help manage the allergic reactions.