To prevent the critical damage to human tissue by the high temperature on an implanted or wearable node, various temperature-aware routing protocols have been proposed in wireless body area networks (WBAN). However, routing-based approaches cannot provide a flexible trade-off between temperature increase and quality-of-service (QoS) degradation because their mechanisms have some potential problems owing to a lack of compatibility with the MAC layer. To address this problem, in this study, we aim to jointly satisfy the temperature constraints and QoS requirements by dynamically managing the available resources at the MAC layer. For this, we use the resource management functions specified in the IEEE 802.15.6 standard. Specifically, we define new upper-layer components and service primitives to control the body temperature in an adaptive manner. In addition, we divide the MAC layer into two sublayers and define the interaction model between the upper-layer components and the MAC sublayers. Under this layered approach, we propose two types of feasible temperature control mechanisms, i.e., decentralized and centralized, to suppress the temperature increase and guarantee the QoS of the critical data. The simulation results when considering a practical network environment prove that, based on the highest-priority node, our approach can achieve an approximately 3.4% higher temperature increase ratio, 9.7% throughput, 19% power consumption ratio, and 12.2% shorter delay compared with a conventional approach.