MAFA is a transcription factor expressed in the pancreas and dorsal root ganglion neurons. The panniculus carnosus, also referred to as the cutaneous trunk muscle, cutaneous trunci, or cutaneous maximus, is a cutaneous muscle situated in the deep layer of human skin. We developed a MAFA-cre mouse and employed morphological and optogenetic techniques to investigate MAFA expression in the skin and its associated functions. Our novel findings indicate that MAFA is expressed in the panniculus carnosus muscles, and activation of these MAFA-expressing muscles induces twitching in the back.