  Complex thermodynamics of the human body and external factors may cause
differences between oral and core body temperatures. We present a 19-subject
study where continuous measurements of ingested core temperature pills are
compared against spot measurements of oral temperature, both FDA-cleared
devices, in free-living conditions. Based on measurements from 419 samples
across 19 subjects, MAE of 0.30 +/- 0.26 oC and 95% limits of agreement of
-0.60 and 0.90 oC was observed between ingestible pill temperature and oral
temperature. These results demonstrate that statistically significant
differences (p<0.001) between oral and core temperature may arise in
free-living conditions. Such clinically relevant differences in temperature
measurements due to complex thermodynamics of heat exchange in the human body,
measurement noise, and other external factors show the intricacies of
interpreting body temperatures measured at different locations.
