Maintaining security of wearable networked health monitoring sensors (Body Sensor Networks (BSN)) is very important for the acceptance and long term viability of the technology. Sensors in BSNs organize themselves into different topologies for efficiency purpose. Securing these topology formation process is of prime importance. In this paper we present two schemes which rely on the novel technique of using physiological values from the wearer's body for securing a cluster topology formation. Traditional schemes for cluster (one of the most commonly used topology) formation were not designed with security in mind and are susceptible to security flaws. The schemes proposed here not only solve the secure cluster formation problem but also do so efficiently by eliminating all key distribution overheads. We analyzed the security of the protocols and tested their accuracy on a prototype implementation developed using Mica2 motes.