Purpose of review
Textbook theory holds that blood pressure (BP) is regulated by the brain, by blood vessels, or by the kidney. Recent evidence suggests that BP could be regulated in the skin.
The skin holds a complex capillary counter current system, which controls body temperature, skin perfusion, and apparently systemic BP. Epidemiological data suggest that sunlight exposure plays a role in controlling BP. Ultraviolet A radiation produces vasodilation and a fall in BP. Keratinocytes and immune cells control blood flow in the extensive countercurrent loop system of the skin by producing nitric oxide, a key regulator of vascular tone. The balance between hypoxia-inducible factor-1α and hypoxia-inducible factor-2α activity in keratinocytes controls skin perfusion, systemic thermoregulation, and systemic BP by nitric oxide-dependent mechanisms. Furthermore, the skin accumulates Na+, which generates a barrier to promote immunological host defense. Immune cells control skin Na+ metabolism and the clearance of Na+ via the lymphatic system. Reduced lymphatic clearance increases BP.
Apart from the well-known role of the brain, blood vessels, and the kidney, the skin is important for systemic BP control in humans and in experimental animals.