Assessment of axillary temperature for the evaluation of normal body temperature of healthy young adults at rest in a thermoneutral environment

Background: The aims of this study were to (1) evaluate whether recently introduced methods of measuring axillary temperature are reliable, (2) examine if individuals know their baseline body temperature based on an actual measurement, and (3) assess the factors affecting axillary temperature and reevaluate the meaning of the axillary temperature. Methods: Subjects were healthy young men and women (n=76 and n = 65, respectively). Three measurements were obtained: (1) axillary temperature using a digital thermometer in a predictive mode requiring 10 s (T _{ax-10 s} ), (2) axillary temperature using a digital thermometer in a standard mode requiring 10 min (T _{ax-10 min} ), and (3) tympanic membrane temperature continuously measured by infrared thermometry (T _ty ). The subjects answered questions about eating and exercise habits, sleep and menstrual cycles, and thermoregulation and reported what they believed their regular body temperature to be (T _reg ). Results: T _reg , T _{ax-10 s} , T _{ax-10 min} , and T _ty were 36.2 ± 0.4, 36.4 ± 0.5, 36.5 ± 0.4, and 36.8 ± 0.3 °C (mean ± SD), respectively. There were correlations between T _ty and T _{ax-10 min} , T _ty and T _{ax-10 s} , and T _{ax-10 min} and T _{ax-10 s} (r = .62, r = .46, and r = .59, respectively, P < .001), but not between T _reg and T _{ax-10 s} (r = .11, P = .20). A lower T _{ax-10 s} was associated with smaller body mass indices and irregular menstrual cycles. Conclusions: Modern devices for measuring axillary temperature may have changed the range of body temperature that is recognized as normal. Core body temperature variations estimated by tympanic measurements were smaller than those estimated by axillary measurements. This variation of axillary temperature may be due to changes in the measurement methods introduced by modern devices and techniques. However, axillary temperature values correlated well with those of tympanic measurements, suggesting that the technique may reliably report an individual's state of health. It is important for individuals to know their baseline axillary temperature to evaluate subsequent temperature measurements as normal or abnormal. Moreover, axillary temperature variations may, in part, reflect fat mass and changes due to the menstrual cycle.