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How Bacteria Are Linked to Allergies


According to epidemiological studies, 20-30% of adults and about 40% of children in the world suffer from allergic rhinitis. Another 300 million people have asthma.

And approximately 10% of the population of developed countries and 6-8% of children under the age of 5 years live with a diagnosis of food allergy. At the same time, since 1997, the number of food reactions among children alone has increased by about 50%.

The prevalence of allergic diseases is explained by such factors as malnutrition, birth method, the presence of relatives with allergies, the use of antibiotics, living conditions in the first year of life, etc. Most of these factors share one common denominator – they are all somehow related to microbes and the microbiome .

Microbiome is a collection of bacteria that live in and on the human body. New data indicate that even those organs that have been considered sterile for quite some time, such as the lungs, still contain various bacteria.

These microorganisms are involved in the synthesis of vitamins, acids, digestion of indigestible fibers.

Moreover, as it is believed today, it is bacteria that play a decisive role in teaching our immune system to distinguish between truly dangerous microorganisms and harmless foreign molecules associated with our diet and environment, which is very important for allergies.

However, while some bacteria help prevent allergic tendencies, others can contribute to it. For example, causing the release of histamine from human basophilic leukocytes and mast cells through IgE -dependent or independent mechanisms.

Several studies show that bacteria can also induce differentiation of naïve T cells into Th2 or Th17 cells and induce the release of cytokines from Th2. Bacterial species such as M. pneumoniae or C. pneumoniae induce the production of IL-4. It is the excess of the latter that is directly related to allergies.

A healthy microbiota can protect against allergic sensitization, however, under conditions of dysbacteriosis, the microbiome can cause an increase in the levels of these pro- inflammatory substances. This leads to a change in the immune environment in the intestine and the emergence of allergies.



One of the most common causes of failure in the human microbiome is antibiotics.

For example, the average child receives three courses of these drugs in the first two years of life. At the same time, taking antibiotics during the first month of life is associated with the occurrence of an allergy to cow’s milk. The use of antibiotics by the mother during pregnancy increases the risk of developing asthma in the child. As well as taking antibiotics by a child during the first year of life.

Studies in mice show that antibiotics can inhibit airway tolerance to airborne allergens. For example, such as spores of fungi (in particular, Aspergillus fumigatus ) or ovalbumin in the form of an aerosol.

At the same time, studies show that certain infections that a person tries to eradicate with antibiotics can serve as protection against allergies.

For example, with the destruction of helminthic invasions, cases of allergic diseases began to increase among the population of developed countries.

Parasitic infections can provide some protection against allergies. This occurs, in particular, by blocking the binding of allergen-specific antibodies to mast cells. Even Helicobacter pylori , a known causative agent of stomach ulcers, may also be beneficial and may prevent the development of asthma. Especially if colonization occurs at an early age.


Another important factor that can influence the microbiome is the way a baby is born. It has been proven that babies born by caesarean section usually have a microbiome rich in staphylococci and streptococci. This, in turn, increases the likelihood of developing allergies, asthma, and gluten intolerance.

In addition, babies born by caesarean section are twice as likely to be sensitized to egg and milk allergens. Overall, according to a Swedish study, caesarean section increases the risk of food allergies by 21%.


Compared with antibiotics and caesarean section, breastfeeding, on the contrary, increases the colonization of the intestines of babies with lacto- and bifidobacteria.

Breast milk, especially colostrum, transmits passive immunity in the form of IgM , IgG , and IgA antibodies from mother to child. IgA is of particular importance in the gut due to its role in the immune response to food antigens and the maintenance of microbiome homeostasis .

Breast milk also contains oligosaccharides and a wide range of fatty acids that positively affect the gut microbiome and its ability to produce metabolites that protect against allergies and asthma. In addition, breast milk contains polyphenols and vitamin D, which are also important for microbiome diversity .

Living conditions and contact with animals

Some research suggests that a diverse gut flora in early childhood is associated with a reduced risk of allergies before the age of 5 years.

Conversely, if the number and diversity of Gram-negative gammaproteobacteria , also common in soil and vegetation, is reduced in the skin of adolescents, this may be indicative of atopy .

These data can be attributed to the so-called hygienic theory of the spread of allergies.

No, it’s not really about personal hygiene or cleanliness in the house. This is that children who were born and grow up in contact with animals (from dogs and cats to cows and horses), as well as with older brothers or sisters, are less likely to get allergies and have a more diverse microbiome due to more frequent contact with various bacteria, the influence of parasites, infections, etc. Conversely, children who live in cities and do not have large families and pets have a greater risk of acquiring allergies due to insufficient stimulation of Th1 cells, which cannot balance the effects of Th2 cells associated with allergies.

Hygiene theory was supplemented by the Western lifestyle hypothesis. Sogasno more recently , an imbalance in the Th2 cell population leads to the production of interleukins (IL-4 and IL-5), which in turn induce the production of IgE and atopy-causing eosinophils .


the gastrointestinal tract has the most diverse microbiome .

Its bacteria play a fundamental role in the formation of human immunity, balancing the activity of Th-1 cells and Th-2 cells involved in allergic reactions.

Poor microbial diversity may be due to low levels of IgA at the intestinal surface barrier.

It can lead to a violation of tolerance to certain foods and, as a result, to the appearancefood allergies and asthma.

In addition, bacteria from the Lachnospiraceae and Ruminococcaceae families produce insoluble fatty acids (SCFAs) such as propionate, butyrate and acetate. They have various anti-inflammatory effects on the immune system and may modulate food allergy and respiratory disease states.

It is noteworthy that by what kind of bacteria live in the human intestine, one can judge a person’s tendency to allergic reactions or the presence of allergies in the past.

For example, if an eight-year-old child has a microbiome enriched with Clostridia and Firmicutes , it is very likely that he outgrew a milk allergy earlier. Some scientists even consider the administration of Clostridium as a potential food allergy prevention.


The gut microbiome can affect other organs as well. Studies in mice have shown that the intestinal epithelial cell is able to form the microbiota and influence the immune response in the respiratory tract.

microbiome may also play a role in stimulating the development of asthma.

Lung colonization occurs gradually, starting with Staphylococcus or Corynebacterium . They are subsequently joined by Moraxella or Alloiococcus . Disruption of microbial population development can lead to changes in the regulation of the IgE -basophil axis with an increase in serum IgE concentration and an increase in the number of circulating basophil populations. As a result, this leads to allergies. And bacteria like Chlamydia trachomatis , Chlamydia pneumoniae and Mycoplasma pneumoniae ; Haemophilus influenzae , Moraxella catarrhalis and streptococcus associated with an increase in the incidence of asthma.

And here is the mixture of Bifidobacterium breve and non- digestible oligosaccharides may, in contrast, inhibit lung airway inflammation by modulating T-cell regulatory response.

Enterococcus may also suppress symptoms of allergic respiratory disease, including asthma. faecalis .


Bacterial dysbiosis is associated with chronic inflammatory skin diseases such as atopic dermatitis and psoriasis.

Newborns with eczema show a decrease in Bacteroidetes and Proteobacteria diversity .

C, Streptococcus or Propionibacterium .

In this case, the age at which changes in the microbiome occur can sometimes play a role . For example, if colonization with S. pneumoniae , H. influenzae , or M. catarrhalis In exacerbations of atopic dermatitis, microorganisms such as E. coli during the first month of life increase the risk of asthma, colonization by this microbe at the age of 12 months no longer leads to such consequences.


One of the possible consequences of dysbacteriosis may be a decrease in the level of short-chain fatty acids SCFA. A low level of SCFA is associated with an allergic phenotype, while an increase in SCFA levels may improve the course of the disease.

healthy probiotic bacteria can help improve your microbiome .

Studies have shown that oral probiotics may prevent eczema and benefit patients with allergic rhinitis. The beneficial bacteria also show some beneficial effects for other allergic diseases, including asthma.

In addition, there is evidence that probiotics can cause desensitization to peanut and milk in 82% of patients when used concomitantly with appropriate sublingual allergen immunotherapy.

Prebiotics may also be helpful . In particular, fiber and oligosaccharides are probiotic nutrients that can improve immunity and metabolism.

In addition, there is evidence that eating enough fiber can suppress the symptoms of allergic rhinitis. And experiments on mice show that the use of prebiotic products by pregnant mice can prevent the appearance of allergies in their offspring.

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