The conversion of sustainable heat sources from the human body into electricity is a promising strategy for self-powered temperature monitoring and power supplies in wearable electronics. Recently, ionic thermoelectrics (i-TEs) have gained considerable attention because of their Seebeck coefficients (mV K-1), which are orders of magnitude larger than those of conventional electronic TEs (e-TEs). In particular, i-TE supercapacitors (ITESCs) based on thermodiffusion under a temperature gradient in redox-free electrolytes exhibit Seebeck coefficients larger than 10 mV K-1. This characteristic solves the requirement for numerous pairs of p/n type TE legs to achieve sufficient output voltage, thereby substantially minimizing device complexity. Therefore, the development of stretchable and wearable ITESCs capable of harvesting human-generated thermal energy is beneficial for future wearable platforms. From this perspective, recent studies have been summarized on stretchable i-TE electrolytes, which hold considerable potential for use in wearable ITESCs and sensors. Furthermore, the challenges of recent ITESCs have been presented, and the perspectives for the development of fully stretchable ITESCs have been provided for future wearable applications.