Chemists in Germany have developed a system that may be able to effectively ‘turn off’ pain-sensitive neurons. They have done this using a chemical compound they call QAQ. The molecule, made up of two parts containing quaternary ammonium connected by a double nitrogen bond, forms a switch that can be altered by light of specific wavelengths. The end of QAQ that resembles lidocaine, a local anesthetic, responds to heat in a way that allows it to filter through endogenous ion channels to get the molecules into nerve cells. While the results of tests of the system in animals prove its analgesic effect, therapeutic application in humans is "a long way off" according to Timm Fehrentz, one of the two first authors on the new paper. Currently, the light that ‘flips the switch’ of the QAQ molecule is unable to penetrate human skin The original press release in German can be found here, and an English version here.