Quantitative and Qualitative Evaluation of the Sweating Function of the Human Earlobe for Heat Stress Monitoring.

Background: This study evaluated thermoregulatory sweating at the earlobe under heat exposure as an initial step toward exploring its potential as a technically interesting candidate site for skin temperature monitoring in occupational heat stress assessment. Methods: Two experiments were conducted in healthy male participants. Sweat rates on the medial and lateral earlobe and forearm were quantitatively measured using ventilated capsule perspiration meters at 25, 30, and 35 °C ambient temperatures with 50% relative humidity. Qualitative sweating was assessed using Minor's iodine-starch test at 40°C ambient temperature and 50% relative humidity. Results: Earlobe sweat rates were consistently and significantly lower than forearm values, with minimal temperature-related variation. No iodine-starch reaction was observed on the earlobe, whereas sweating was detected on the auricle and face. Conclusion: The earlobe appeared to exhibit negligible thermoregulatory sweating under the tested conditions. Given the low likelihood of sweating-related interference, the earlobe may warrant further investigation as a technically interesting candidate site for future validation studies of skin temperature monitoring in occupational heat stress assessment.