# Surface and intradermal temperature responses of adults to ambient heat stress with and without cooling

## TL;DR

This study compares skin surface and intradermal temperatures in adults under heat stress with and without cooling methods.

## Contribution

The study reveals how cooling methods affect skin temperature measurements differently at the surface and intradermally.

## Key findings

- Intradermal temperature was lower than surface temperature during ambient heating.
- Cooling methods like fan and water spray altered the relationship between surface and intradermal temperatures.
- Water spray lowered surface temperature more than intradermal temperature.

## Abstract

Accurate measurement of skin temperature is crucial to understanding responses to heat. We tested the hypothesis that intradermal temperature would differ from skin surface temperature during ambient heating with and without fan and water spray (24°C). Nine healthy adults rested in an environmental chamber maintained at 40°C and 15% relative humidity with and without fan, fan + water spray, and water spray. We assessed temperature in the dermal space (intradermal) and on the skin surface (surface) using thermocouple microprobes. In addition, we measured skin temperature using a standard uninsulated thermocouple taped to the skin (standard). During heating intradermal (35.3 ± 0.6°C) was lower than standard (35.9 ± 0.5°C; p = 0.005), but not surface (36.0 ± 0.7°C; p = 0.056) temperature. With the fan, intradermal (36.9 ± 0.5°C) was lower than both surface (37.8 ± 0.7°C; p < 0.001) and standard (37.4 ± 0.5°C; p = 0.005) temperature. With fan + water spray, intradermal (32.3 ± 1.5°C) was higher than standard (30.3 ± 2.2°C; p = 0.022), but not different from surface (30.8 ± 1.7°C; p = 0.125) temperature. With water spray alone, intradermal (31.9 ± 1.4°C) was higher than both surface (30.6 ± 1.7°C; p = 0.035) and standard (30.4 ± 1.3°C; p = 0.031) temperature. In the heat, skin temperature measured on the surface is higher than intradermal temperature. When cool water was applied to the skin, surface temperature was lower than intradermal temperature.