7 Menstrual Cycle & Thermoregulation

Phase-Specific Thermoregulatory Changes

The menstrual cycle involves recurring shifts in hormone levels, particularly estradiol and progesterone, which influence how the body regulates temperature. These hormonal fluctuations affect resting core temperature, sweat onset, and vascular responses.

Figure 2. Core body temperature across the menstrual cycle. This figure illustrates the typical rise in core body temperature following ovulation, corresponding with the onset of the luteal phase. The follicular phase is associated with lower baseline temperatures, which increase by approximately 0.3 to 0.5°C after the luteinising hormone (LH) surge.

Menstrual Phase (Days 1–5)

• Hormone levels are at their lowest

• Core temperature is typically at its baseline

• Thermoregulatory responses are stable but not significantly altered

Follicular Phase (Days 6–14)

• Estradiol rises gradually and peaks just before ovulation

• This promotes:

  • Lower core temperature

  • Earlier onset of sweating

  • Increased skin blood flow (vasodilation)

• Thermoregulation is more sensitive and efficient, improving tolerance to heat

Studies show women in the follicular phase begin sweating at a lower body temperature compared to other phases

Ovulation (~Day 14)

• A surge in luteinising hormone (LH) triggers ovulation

• Estradiol peaks, followed by a quick dip

• Progesterone begins to rise, initiating thermogenic effects

Luteal Phase (Days 15–28)

• Progesterone dominates

• Core body temperature rises by 0.3 to 0.5°C

• Sweat threshold increases, and skin vasodilation is delayed

• This phase is associated with reduced heat dissipation capacity

In warm environments or during exercise, this may increase risk of heat strain or dehydration.

Why This Matters

These thermoregulatory shifts have implications for:

• Heat tolerance during different cycle phases

• Exercise performance and risk of overheating

• Occupational safety in hot environments

• Clinical monitoring during fertility tracking or heat-sensitive medical conditions

Recap

• The follicular phase supports better cooling through estrogen

• The luteal phase promotes heat retention due to progesterone

• These shifts affect core temperature, sweat rate, and vascular responses across the cycle