The largest microbial population, the gut microbiome, is in contact with epithelial, immune, endocrine and nerve cell mucosal surfaces that all senses and reacts to microbial signals. These reciprocal interactions result in a practical interplay of microbes with human physiology. Examples of coadaptation are Bifidobacteria and Bacteroides, the anaerobic compounds which have adjusted their metabolism to human milk and to the immune development of infants, which have developed to rely on the presence of beneficial microbes. Research currently has shown that the unique composition of the early-life intestinal microbiota aligns with host immunity maturation. Distortions in normal microbial successions during intestinal colonisation, like atopy and asthma, are a consistent characteristic of immuno medical diseases. The study catalogues and sums up evidence of the importance of gut microbiome as an etiological determinant of immune-mediated allergic diseases and records recent birth cohorts documenting associations between immune and microbial alterations.

The molecular function of early life microbiome in atopy and asthma susceptibilities has become indispensable to ecological principles that characterise microbial dynamics in the host environment and to the concept of immune and neuro-endocrine signals caused by host-microbiome interactions.