Wet cupping therapy (WCT) is a simple and economic treatment that still needs scientific interpretation. It treated effectively diseases with different etiologies and pathogeneses e.g. rheumatoid arthritis (RA), hypertension, migraine, carpal tunnel syndrome (CTS), fibromyalgia, cellulitis and others. Here, we review medical and scientific bases underlying cupping therapy and introduce Taibah theory as a novel evidence-based scientific mechanism to explain it. Briefly, in Taibah theory, WCT is a minor surgical excretory procedure related scientifically to the principles of renal glomerular filtration and abscess evacuation, where a pressure-dependent excretion of causative pathological substances (CPS) occurs. CPS include disease-causing substances and disease-related substances (that result during disease pathogenesis). Negative pressure applied to skin surface causes local collection of filtered and interstitial fluids containing CPS at skin upliftings inside cups. Scarifying skin upliftings followed by cupping causes a pressure gradient and a traction force across the skin and capillaries to excrete collected fluids with CPS and cause bleeding at puncture sites. This increases filtration at both capillary ends and causes clearance of blood and interstitial spaces from CPS. WCT benefits from the suction pressure, phenomenon of reactive hyperemia, nitric oxide production and skin scarifications (openings in skin barrier) in enhancing natural excretory skin functions, improving lymphatic and capillary circulations and restoring homeostasis. Reported CPS of RA include autoantibodies, immune complexes, soluble interleukin-2 receptors, inflammatory mediators, certain cytokines, prostaglandins, toxic cellular products and rheumatoid factor, while CPS of CTS include malondialdehyde, interleukin 6, prostaglandin PGE- 2 and progressive edema (causing pain). WCT-induced filtration pressure may excrete those CPS in cupped blood.