Skin-based touch input opens up new opportunities for direct, subtle, and expressive interaction. However, existing skinworn sensors are restricted to single-touch input and limited by a low resolution. We present the first skin overlay that can capture high-resolution multi-touch input. Our main contributions are: 1) Based on an exploration of functional materials, we present a fabrication approach for printing thin and flexible multi-touch sensors for on-skin interactions. 2) We present the first non-rectangular multi-touch sensor overlay for use on skin and introduce a design tool that generates such sensors in custom shapes and sizes. 3) To validate the feasibility and versatility of our approach, we present four application examples and empirical results from two technical evaluations. They confirm that the sensor achieves a high signal-to-noise ratio on the body under various grounding conditions and has a high spatial accuracy even when subjected to strong deformations.