Narrative Review on Infants' Thermoregulatory Response to Heat

Infants are at a higher risk of heat-related morbidity and mortality compared to children and adults. However, it remains unclear whether this vulnerability stems from immature thermoregulatory mechanisms or simply from their dependence on caregivers. This narrative review examines current literature on infant thermoregulation during heat exposure and explores how unique physiological characteristics may influence vulnerability. Key differences in infants compared to older individuals include their larger surface area-to-mass ratio, which (1) facilitates heat dissipation when skin temperature exceeds ambient temperature, but compromises heat loss in reversed conditions, and (2) likely enables a large portion of an infant's blood volume to shift to the skin, promoting heat loss but reducing blood volume in the central circulation. Infants also have a relatively high metabolic heat production. Additionally, their lower sweat output per gland may represent either a limitation or a different thermoregulatory strategy. Contrary to common assumptions, most components of infants' thermoregulatory system do not appear inherently immature; rather, their distinct physiological characteristics-combined with their reliance on caregivers-shape how and when heat exposure may become harmful. Nevertheless, further research is needed to better understand how these interacting factors influence infants' ability to maintain stable core temperature. Meanwhile, coordinated efforts by caregivers, health professionals, and policymakers are essential to minimize infants' heat-related health risks.