Never heard of this before. From NIH:
Multi-disciplinary research has revealed that electrically conductive contact of the human body with the surface of the Earth (grounding or earthing) produces intriguing effects on physiology and health. Such effects relate to inflammation, immune responses, wound healing, and prevention and treatment of chronic inflammatory and autoimmune diseases. The purpose of this report is two-fold: to 1) inform researchers about what appears to be a new perspective to the study of inflammation, and 2) alert researchers that the length of time and degree (resistance to ground) of grounding of experimental animals is an important but usually overlooked factor that can influence outcomes of studies of inflammation, wound healing, and tumorigenesis.
Grounding or earthing refers to direct skin contact with the surface of the Earth, such as with bare feet or hands, or with various grounding systems. … Various grounding systems are available that enable frequent contact with the Earth, such as while sleeping, sitting at a computer, or walking outdoors. These are simple conductive systems in the form of sheets, mats, wrist or ankle bands, adhesive patches that can be used inside the home or office, and footwear. These applications are connected to the Earth via a cord inserted into a grounded wall outlet or attached to a ground rod placed in the soil outside below a window. For the footwear applications, a conductive plug is positioned in the shoe sole at the ball of the foot, under the metatarsals, at the acupuncture point known as Kidney 1. From a practical standpoint, these methods offer a convenient and routine, user-friendly approach to grounding or earthing.
Maybe this explains why I love beach vacations so much.