Outer sickness radical, a pictograph of a person reclining on a bed (originally
爿 'bed' rotated). It marks
痕 as something on the body — originally a scar, the lingering trace of an injury or disease. From 'scar' the meaning generalised to 'mark, trace, vestige' of any kind (
痕迹 trace,
伤痕 scar). The radical anchors the whole illness family:
病,
疼,
痛,
疲,
痒,
疯.