Predicting Deep Body Temperature (T) from Forehead Skin Temperature: T or Not T?

There is a need to rapidly screen individuals for heat strain and fever using skin temperature (T) as an index of deep body temperature (T). This study's aim was to assess whether T could serve as an accurate and valid index of T during a simulated heatwave. Seven participants maintained a continuous schedule over 9-days, in 3-day parts; pre-/post-HW (25.4 °C), simulated-HW (35.4 °C). Contact thermistors measured T (T, T); radio pills measured gastrointestinal temperature (T). Proximal-distal temperature gradients (ΔT) were also measured. Measurements were grouped into ambient conditions: 22, 25, and 35 °C. T and T only displayed a significant relationship in 22 °C (r: 0.591; < 0.001) and 25 °C (r: 0.408; < 0.001) conditions. A linear regression of all conditions identified T and ΔT as significant predictors of T (r: 0.588; F: 125.771; < 0.001), producing a root mean square error of 0.26 °C. Additional residual analysis identified T to be responsible for a plateau in T prediction above 37 °C. Contact T was shown to be a statistically suitable indicator of T in non-HW conditions; however, an error of ~1 °C makes this physiologically redundant. The measurement of multiple sites may improve T prediction, though it is still physiologically unsuitable, especially at higher ambient temperatures.