Conductive hydrogel-based epidermal sensors are attracting significant interest due to their great potential in soft robotics, electronic skins, bioelectronics and personalized healthcare monitoring. However, the conventional conductive hydrogel-based epidermal sensors cannot be degraded, resulting in the significant problem of waste, which will gradually increase the burden on the environment. Herein, degradable adhesive epidermal sensors were assembled using conductive nanocomposite hydrogels, which were prepared via the conformal coating of cellulose nanofiber (CNF) networks and supramolecular interaction among CNF, polydopamine (PDA), Fe³⁺, and polyacrylamide (PAM). They exhibited superior mechanical properties, reliable degradability (30 days in water), and excellent self-adhesiveness. The obtained hydrogels could be assembled as self-adhesive, degradable epidermal sensors for real-time human motion monitoring. Air could be sucked into the hydrogels during their swelling process, thereby oxidizing the tris-catechol–Fe³⁺ complexes and releasing Fe³⁺. Finally, the polymer networks were degraded via a Fenton-like reaction dominated by S₂O₈²⁻ and Fe(II/III) with the help of the catechol groups of PDA. This work paves the way for the potential fabrication of degradable, and self-adhesive epidermal sensors for applications in human–machine interactions, implantable bioelectronics, and personalized healthcare monitoring.