Uremic pruritus (UP) is a frequent phenomenon and it is regarded as one of the most bothersome symptoms in patients with chronic renal disease. The prevalence of UP is still high and reported in around 40% to 50%. UP has an important impact on patients' quality of life and sleep, depression, and increased mortality. The pathogenesis of UP remains blurry, although many different factors have been indicated in the etiology of this symptom, including increased systemic inflammation, abnormal serum parathyroid hormone, calcium, and phosphorus levels, an imbalance in opiate receptors, a neuropathic process, or even skin dryness. This is why until now there is no specific treatment for patients with UP and many of the available therapeutic modalities are not satisfactory Pruritus in liver diseases can often be a debilitating symptom causing significant impairment in quality of life. Not all patients with liver disease develop pruritus and its prevalence varies depending on the underlying cause of liver disease. It is more common in conditions characterized by bile duct inflammatory destruction than in those characterized by hepatocellular injury.~Cutaneous microbiota delivers a diverse and far-reaching influence on our physiology by calling upon the host nervous system. Bacteria make metabolites, toxins, and structural components that are recognized by peripheral and central neurons via matching receptors. Microbiota also indirectly affects neural function by causing endocrine (i.e., keratinocytes) and immune cells to transmit signals (i.e., cytokines, proteases). Itch is a prototypic sensory neural function, and the microbiota propels the itch-scratch cycle.
Various neurotransmitters may share in the pathogenesis of hepatic and renal itching.~Skin microbiota may share in the pathogenesis of pruritus.