IoT architectures involve people who use these IoT devices and should contribute and cooperate with IoT systems synergistically. Therefore, IoT architectures must be aware of the human context and consider people as an essential part of the system. IoT can support healthcare systems and allow people to stay at home and be supervised in real-time, instead of being sent to nursing homes or clinics [2]. Numerous IoT architectures incorporate personal healthcare devices (PHDs) for remote patient monitoring. These devices are portable systems with relevant features for patient biomedical signal sensing and measurement. The number of PHDs are increasing and must incorporate efficient methods for healthcare servers' connection [10; 11]. PHDs are used for activity, blood pressure and pulse oximeters monitoring, medication dispensers, and fall detection [12; 13]. These portable devices are used in IoT environments by healthcare staff and allow patient monitoring at home. Moreover, healthcare systems cannot be designed and implemented without the relevant role of PHDs. Moreover, PHDs' integration in healthcare environments is proposed by several studies [14; 15; 16]. Several monitoring activities, such as measuring cardiac frequency and blood pressure, that in the past were only available at the hospital, can now be continuously performed by using wearable sensors incorporated in, e.g., smartwatches. However, hospital measurements cannot be completely replaced with wearables, such as smartwatches, for several reasons, such as reliability, accuracy, and the context of the measurement. These wearable sensors should be used as an important complement and will never replace human integration and the relationship between the doctor and the patient. Healthcare solutions that allow real-time monitoring can avoid unplanned hospitalizations that result in expensive emergency costs. IoT incorporates several advantages for the design and development of healthcare systems. IoT can provide networks of connected devices, Cloud applications, and services to facilitate the patient's monitored data transmission and storage. IoT applications are closely related to healthcare systems through remote monitoring, smart-homes, wearable devices, and smart medical equipment. Numerous academic and industry research studies have been conducted about IoT interoperability and therefore several methods and technologies to address interoperability challenges are available in the literature. These methods focus on the standardization of communication protocols to provide interoperability of heterogeneous devices, networks, and data structures. Therefore, these methods and technologies can also be applied to IoT in order to provide interoperability to the healthcare domain. Furthermore, numerous applications for healthcare have been developed based on IoT, which demonstrates the relevant advantages of this architecture to provide efficient and cost-effective healthcare systems [17]. In order to support high-quality healthcare systems, IoT must adopt standardization, including efficient wireless protocols, improved mobile and wearable sensors, and cost-effective and low-power microprocessors [18]. A study presented by [19] demonstrates that individual approval of IoT advances are broad and growing. The current accessibility of remote wireless medical systems and the emerging diffusion of electronic healthcare database records can make the IoT communication framework the fundamental empowering agent for distributed ubiquitous healthcare applications [20]. This paper aims to provide an introduction to healthcare systems, review the current state of the art, and focus on the technologies, applications, challenges, opportunities, IoT open-source platforms, and operating systems. At this stage, a comprehensive understanding of IoT from a healthcare background is significant in order to support future research.