On an ordinary fair-weather day, over flat desert or open sea, the electric potential climbs about 100 volts for every metre you rise, and the direction of that field means the Earth's surface carries a negative charge. Add it up to the top of the atmosphere and it comes to roughly 400,000 volts, kept topped up by the world's thunderstorms, whose lightning mostly carries negative charge down to the ground. [1]

So why doesn't the sky zap your nose, sitting some 200 volts "above" your feet? Because you are a fairly good conductor. In Feynman's words, "you and the ground will tend to make one equipotential surface." The field bends around you like a blanket, and your head and feet end up at very nearly the same potential. To the atmosphere, a person standing on the ground is just a small walking bump in it. [1]

Earthing research asks what that connection does in the body, usually via conductive patches, mats or sheets wired to a rod in the soil. The studies are real but small: a 12-person pilot where eight weeks of grounded sleep came with lower night-time cortisol and reports of better sleep and less pain; a 10-person study where two hours grounded raised red-blood-cell surface charge and reduced clumping in fingertip samples; an 8-person pilot on post-exercise muscle soreness. [2–5]

The authors of the 2015 inflammation review say it plainly: "most of these pilot studies involved relatively few subjects." They also disclose that they work as contractors for EarthFx, the company sponsoring the research, and two of the three hold shares in it. Intriguing and early, then. Worth our curiosity, not a promise. [5]