Fig. 1.

The brain-intestinal axis and SSRI. The brain-intestinal axis is a bidirectional communication system between the central nervous system (CNS) and the gastrointestinal tract. SSRIs can affect the microbiota. The microbiota can regulate the CNS function mainly through the neuroimmune and neuroendocrine systems. Bacteria in the intestines can produce various types of neurotransmitters that regulate host immune cell function via the nervous system. The intestinal microbiome can also influence skin homeostasis by regulating the coordinated differentiation of the epidermis and immune system function