With increasing interest in the usage of wearable wireless communication technologies at 1.8 & 2.4GHz and 5 & 8.9GHz band of frequencies, investigations on the human body interaction with these devices are becoming important. This paper provides a microstrip-based multi-band monopole antenna for body Wearable Wireless Devices (WWD), covering licensed and license-free wireless technologies at UHF/UWB when placed on human body. Five parts of the body were considered to evaluate the electromagnetic (EM) effects on the body. Specific Absorption Rate (SAR) values were found to range from 0.09-0.25 W/kg by using numerical modeling. The thermal effects were investigated experimentally using infrared thermography, and temperature changes not exceeding 1°C were noticed. Analyses of numerical, simulated and experimental results show that infrared thermography, a temperature-based technique, can be used to evaluate the compliance of WWDs with safety exposure limits for various wireless applications.