8 Heat Stress Across the Female Lifespan

From Menstruation to Menopause

Across the lifespan, shifts in sex steroid hormones shape how the body manages heat. These changes impact core temperature regulation, heat dissipation, and sensitivity to heat-related illness. Understanding these patterns helps explain why heat affects menstruating individuals, pregnant women, and postmenopausal women differently.

Menstruation and Adolescence

During puberty and early reproductive years:

• Estradiol and progesterone levels begin to cycle regularly

• This introduces the phase-dependent thermoregulatory shifts covered in the previous chapter (see Figure 2)

• Adolescents may experience more dramatic temperature swings, especially as hormonal rhythms stabilise

Clinical relevance:

• Teens may be especially vulnerable during the luteal phase, when progesterone impairs heat dissipation

• Some evidence suggests that cycle irregularity in early adolescence may affect consistency of thermoregulation

Pregnancy

Pregnancy presents a unique thermophysiological challenge:

• Progesterone remains chronically elevated, maintaining a higher thermoregulatory set point

• The fetus generates its own heat, increasing maternal metabolic load

• Skin blood flow is already elevated, leaving less capacity to further vasodilate in response to heat

• Plasma volume increases, but sweat thresholds rise, leading to reduced evaporative cooling

Thermal sensitivity in pregnancy is not only higher, but it is phase-specific:

• Early gestation: thermoregulatory strain may affect implantation and placentation

• Mid to late pregnancy: increased cardiovascular and fluid demands heighten the risk of overheating

• Third trimester: thermoregulation is shared with the fetus, whose core temperature is often 0.3 to 1°C higher than the mother’s

Research suggests that heat stress may contribute to adverse outcomes such as preterm birth, low birthweight, and stillbirth, particularly in the second and third trimesters

Menopause

After menopause:

• Estradiol and progesterone levels drop sharply

• Thermoregulatory set point becomes unstable

• Many women experience vasomotor symptoms, most notably hot flashes

A hot flash is:

• A sudden vasodilatory response

• Triggered by small increases in core body temperature

• Mediated by unstable hypothalamic set points and reduced feedback inhibition

These symptoms:

• Are often worse in warm climates

• Can be exacerbated by nighttime temperature fluctuations, affecting sleep

• Improve with estradiol therapy, which helps stabilise set point regulation

Recap

• Hormonal changes across the lifespan alter the body’s thermal control system

• Adolescents, pregnant individuals, and postmenopausal women each have distinct thermal vulnerabilities

• In pregnancy, the ability to offload heat is reduced despite increased thermal load

• After menopause, declining hormones contribute to dysregulated thermoregulatory control