OPRK1 and hyperparathyroidism: Among others, mediators such as histamine or serotonin, dysregulation of the activity of opioid pathways (including kappa-opioid receptor (KOR) downregulation), xerosis, hyperparathyroidism, accumulation of uremic toxins, and dysregulation of the immune system are suspected to be significant factors of chronic itch [4,6,7].