Hot weather and the overheating of indoor spaces can pose a health risk to anyone if adequate protection against high temperatures is not ensured. However, various physiological and health-related factors that impair the body’s ability to regulate temperature can increase the risk of adverse health effects.
Older age (over 65 years)
Serious health effects (need for medical care, mortality) during heatwaves occur mainly among people over the age of 65. Age-related physiological changes weaken the body’s capacity to regulate temperature and reduce the ability to sense heat and thirst. The risk of adverse effects is further increased by chronic illnesses and medications, which are common in older adults. In addition, older people may have physical, cognitive, or psychological functional impairments that make it harder to protect themselves from heat.
Infants and young children (under 5 years)
Young children do not yet have fully developed temperature regulation. Due to their small body size and relatively large skin surface area, they are more susceptible to heat stress and dehydration. The risk is further increased by their higher level of physical activity. Children are also less able to recognize the symptoms of heat stress and take protective actions.
Poor health status and reduced functional capacity
Chronic diseases and severe acute illnesses reduce the body’s ability to tolerate heat stress. Both the conditions themselves and medications used to treat them (e.g., drugs affecting fluid and electrolyte balance or the cardiovascular system, anticholinergic medicines) may impair thermoregulation and functional capacity, limiting the ability to protect oneself from heat. Risk factors include, for example:
- Cardiovascular diseases
- Chronic respiratory diseases
- Diabetes
- Thyroid disorders
- Kidney diseases
- Cognitive disorders
- Mental health disorders
- Substance use disorders
- Severe developmental disabilities
- Certain rare diseases, such as severe ichthyosis, hypohidrotic ectodermal dysplasia, and cystic fibrosis
- Physical disabilities
Sex
Women are physiologically somewhat more sensitive to the harmful effects of heat, as thermoregulation is slightly less efficient and sweating capacity is lower compared to men.
Pregnancy and breastfeeding
During pregnancy, the body’s heat production and need for fluids increase, which raises the risk of heat illnesses. Heat stress increases the risk of pregnancy complications, preterm birth, low birth weight, congenital anomalies, as well as miscarriage and stillbirth. Breastfeeding also increases the mother's risk of dehydration.