Plasma is the fourth state of matter. Most of it burns hotter than a jet exhaust. One version is cool enough to hold against an open wound. Cold atmospheric plasma exploits a thermodynamic loophole. Apply a strong electric field to a gas and the electrons, being roughly two thousand times lighter than the ions and neutrals around them, accelerate almost instantly. They reach one to ten electronvolts, equivalent to tens of thousands of kelvin. The heavy particles barely respond, since each collision transfers only a minute fraction of that energy. The discharge ends up electronically ferocious and thermally mild, sitting near forty degrees Celsius where it meets skin. The therapy is chemistry, not heat. Feed gas and ambient air are cracked into reactive oxygen and nitrogen species, delivered alongside photons, charged particles and transient electric fields. - Atomic oxygen, singlet oxygen and hydroxyl radicals oxidise bacterial membranes and strip cell walls - Nitric oxide signals a...