Local differences in sweat secretion from the head during rest and exercise in the heat

Area of Science:

• Physiology
• Thermoregulation
• Human Heat Exchange

Background:

• The head plays a crucial role in body heat dissipation, especially in hot environments.
• Local variations in sweat secretion across the head surface are not well understood.

Purpose of the Study:

• To investigate the intra-segmental distribution of head sweating.
• To quantify sweat rates at various sites on the head under controlled heating and exercise conditions.

Main Methods:

• Ten healthy males underwent passive heating and exercise-induced hyperthermia in a controlled environment (36°C, 60% RH).
• Sweat rates were measured using ventilated sweat capsules (3.16 cm²) on the forehead and nine sites within the hairline.
• Core temperature and heart rate were monitored, with core temperature peaking at 39.2°C and heart rate at 175 bpm.

Main Results:

• Sweat secretion increased linearly with work rate and core temperature in both hairy and non-hairy head areas.
• The mean sweat rate within the hairline during exercise was 1.95 mg cm⁻² min⁻¹.
• Sweat rates were not uniform; the top of the head had significantly lower sweat rates (30% of forehead) compared to the anterior lateral aspect (P < 0.05).

Conclusions:

• Observed differences in head sweating may be due to local adaptation of eccrine glands.
• Variations could be influenced by factors related to bipedal locomotion affecting forehead evaporation.
• Hidromeiotic suppression might impact sweat glands within the hairline, contributing to regional differences.