A perspective on CO₂ gas sensing — from environments to the skin interface

Carbon dioxide (CO₂) is a universal indicator of biological, chemical, and physiological processes, yet it plays a multifaceted role, from regulating global climate to reflecting human cellular activities. The accurate and continuous measurement technologies of CO₂ have evolved along separate paths: environmental CO₂ monitors to biomedical sensors for respiratory or blood gas assessment. While environmental monitoring and clinical capnography are well established, translating these technologies to continuous, non-invasive transcutaneous CO₂ (tcCO₂) sensing remains challenging due to skin-interface instability, humidity interference, and diffusion-limited transport. This perspective will discuss design principles from ambient CO₂ sensors with emerging materials and architectures for wearable tcCO₂ platforms. This perspective also discusses sensor technologies and methods, their integration into systems, the physiological and skin-interface challenges, and the engineering trade-offs for wearables. We also outline recent advances, identify key gaps, and propose a roadmap for future wearable CO₂ sensors for transcutaneous monitoring.