The rapid development of ultra-thin electronic skins (e-skins) – also called epidermal electronics or electronic tattoos – is opening new realms of possibility for flexible and stretchable monitoring gadgets that are wearable directly on the skin. These e-skin devices can be used for, among other things, prosthetics and rehabilitation, optogenetics, human-machine interfaces, human-computer interaction in gaming, and as diagnostic tools in the medical field (read more on this topic in « Lab-on-skin: Nanotechnology electronics for wearable health monitoring »).