With the advancement of information technology and a shift toward healthcare focused on chronic diseases, health awareness has increased. This trend has driven the development of electronic health records (EHRs). However, traditional EHRs remain confined to individual hospital databases, restricting data sharing across institutions. Therefore, we adopt the concept of personal health records (PHRs), where personal medical records are securely stored in the cloud healthcare under the individual’s ownership, allowing both individuals and authorized medical institutes to access and manage the data in real time. We propose an access control mechanism for cloud-based medical information systems. Our mechanism incorporates time-based authentication to increase access security. Leveraging sensor-generated data, and with the patient’s permission, hospitals can access medical records when the patient goes to different medical institutions. This process ensures practical PHR data transfer within the healthcare network. Conversely, patients can also access their own PHRs with hospital authorization. This approach alleviates both time and costs associated with information transfer. Sensor-generated data further support real-time monitoring. This capability allows medical institutions to promptly access cases on the cloud medical information system for diagnosis and treatment in emergencies.