This document discusses applications of wireless sensor networks in healthcare and related challenges. It describes how wireless sensor networks are being used for vital sign monitoring in hospitals, at-home and mobile health monitoring, and assistance with motor and sensory decline. Examples discussed include monitoring systems called CODEBLUE, HEALTHGEAR, and AMON. It also discusses an epilepsy monitoring smart clothing system called WEMU and a wearable health care system called WEALTHY. The document outlines challenges at the physical, MAC, network, transport and application layers and security threats involving confidentiality, integrity and availability. Physical layer challenges include bandwidth limitations while security threats include eavesdropping, traffic analysis and denial of service attacks.