A notable technology in this regard is customized electronic (e-) skin that can be mounted directly on human skin with tailored design depending on its purpose, attached body part, and user's body shape. [3] Since skin contains various physiological data (e.g., electrophysiological signals, sweat chemistry, and pulse rate) such skin-attached e-skin can interpret the health state of the user. [4,5] Moreover, chronic muscular disease such as inflammatory myopathies and myofascial pain syndrome can be treated with electrical/ thermal stimulation using e-skin. [4,6] Currently, customized e-skins are usually made by patterning and/or printing metal, [3] 1/2D materials, [7] and organic materials [8] on supporting substrates using conventional fabrications strategies such as nozzle printing, [9] screen printing, [10] and lithography [11] in a laboratory or factory. However, devices fabricated in this manner suffer from: 1) limited scalability and flexibility in their design, incapable of on-the-spot implementation, 2) limited durability (i.e., low toughness causing easy tear-off), stretchability, disposability, and gas-permeability (i.e., non-breathability due to the presence of substrate covering the skin), Conventional electronic (e-) skins are a class of thin-film electronics mainly fabricated in laboratories or factories, which is incapable of rapid and simple customization for personalized healthcare. Here a new class of e-tattoos is introduced that can be directly implemented on the skin by facile one-step coating with various designs at multi-scale depending on the purpose of the user without a substrate. An e-tattoo is realized by attaching Pt-decorated carbon nanotubes on gallium-based liquid-metal particles (CMP) to impose intrinsic electrical conductivity and mechanical durability. Tuning the CMP suspension to have low-zeta potential, excellent wettability, and high-vapor pressure enables conformal and intimate assembly of particles directly on the skin in 10 s. Low-cost, ease of preparation, on-skin compatibility, and multifunctionality of CMP make it highly suitable for e-tattoos. Demonstrations of electrical muscle stimulators, photothermal patches, motion artifact-free electrophysiological sensors, and electrochemical biosensors validate the simplicity, versatility, and reliability of the e-tattoo-based approach in biomedical engineering.