With increasing interest in the usage of wearable wireless communication technologies at UHF (0.3-3 GHz) and UWB (3.1-10.6 GHz) frequencies, investigations on the human body interaction with these devices is becoming important. This paper provides a Microstrip based multi-band monopole antenna for Body Wearable Wireless Devices (BWWD), resonating at 1.8 GHz, 2.4 GHz, UWB frequencies, covering licensed and license-free wireless technologies when placed on human tissues. Five body parts are considered to evaluate the biological effects of the radiations on the body. Specific Absorption Rate (SAR) values were found to range from 0.09-0.25 W/kg on the skin, by using numerical modeling. The thermal effects were analyzed and compared between numerical, simulated and experimental results. Experimental investigations were carried out using Infra-red thermography. Temperature rise was observed to be less than 1° C in all the approaches. Analyses show that Infrared thermography, a temperature-based technique can be used to evaluate the compliance of wearable devices with safety exposure guidelines for various wireless applications.