In the human gut microbiota, each group of bacteria has different functions. Histamine is produced by bacteria that are members of the histaminergic microbiota. Primarily; anaerobic spore-forming bacteria such as Clostridium spp. and members of the Enterobacteriaceae family, including Enterobacter spp., Hafnia alveii, Klebsiella spp., Serratia spp., and Escherichia spp. When the numbers of all or some of these bacteria increase in the gut microbiota, they produce excessive amounts of histamine, which can then pass into the bloodstream and trigger systemic allergic reactions.

The biological nature of allergic reactions is fundamentally based on the inflammatory response. So, the external appearance of an allergy is the allergy itself, and its essence is the inflammatory responses.
There are bacteria in the gut microbiota associated with the activation of the inflammatory response: Mainly; Citrobacter spp., Enterobacter spp., Escherichia spp., Klebsiella spp., Providencia spp., Pseudomonas spp., Serratia spp., Sutterella spp.

The increase in the number of these bacteria in the gut microbiota triggers and exacerbates inflammation. In allergic reactions, the histaminergic microbiota and the inflammation-triggering microbiota work together, and some bacterial species are common to both pathways. So the same type of bacteria is responsible for both histamine production and the inflammation response at the same time.
The root cause of allergies and the inflammation activation that underlies them is the imbalance in species diversity and numerical equilibrium in the human gut microbiota. In treatment and follow-up approaches for allergic and acute-chronic inflammatory diseases, the current state of the human gut microbiota should be determined, and the disrupted microbial balance should be restored.
In this context, very positive clinical results are achieved with evidence-based, personalized, and holistic medical practices.