As many devices for human utility target fast and convenient communications with users, superb electronic devices have been demonstrated as hardware for Human-Machine Interface (HMI) in wearable forms. Wearable devices for daily health-cares and self-diagnosis desire more human-like properties unconstrained to deformation. In this sense, stretchable ionics based on flexible and stretchable hydrogels is on the rise as another field to develop wearable devices for bio-applications due to two major reasons; i) ionic currents, choosing the same signal carriers with biological areas, and ii) the adoption of hydrogel ionic conductors which are intrinsically stretchable materials with bio-compatibility. Here, forte and current status of stretchable ionics as well as future applications whose positive effects can be magnified by stretchable ionics are going to be introduced.