Thermoregulation in Children

Letters to the Editor regarding the article Heat Exposure and the Risk of Emergency Hospitalization in Germany Stratified Analyses by Age, Sex, and Diagnostic Group by Hedi Katre Kriit, Alina Herrmann, Raeleesha Norris, Joacim Rocklöv, Manuela De Allegri in issue 26/2025

The authors statistically verified that children, older persons, and persons with certain pre-existing disorders were particularly vulnerable to periods of heat, and the risk of emergency hospital admission increases as a result (1). In the section entitled “Health effects” the authors provide examples of the vulnerability of these groups to heat. From a physiological perspective, however, the following statement is subject to disagreement: “Children, for example, have a less favorable ratio of body surface area to body mass, which hampers heat dissipation […]”. The reference (2) that the authors cited in support, however, contradicts this statement: “They [the young children] had a greater body surface area-to-mass ratio than the mothers by 64 %, which indicated that they had advantages for thermal regulation.”

The younger the child, the greater the body surface area-to-mass ratio. This facilitates the release of heat from the body. Accordingly, small children at rest in comfortable conditions require a higher specific energy turnover (W/kg) than adults to maintain their normal core body temperature. In principle, heat exchange with the environment is bidirectional, which means that the heat balance is always the result of heat loss and heat gain. Under heat conditions, the body surface area-to-mass ratio does not hamper heat loss but facilitates heat gain, which means that the net effect is a rise in the core body temperature. On the other hand, thermoregulation can compensate for this disruption more easily if the body surface area-to-mass ratio is greater, as shown in adults (US soldiers) (3).

In childhood, the wide developmental range hampers the scientific rationale for heat vulnerability. It seems plausible, however, that thermoregulation in some children, especially younger ones, does not optimally cope with the larger—and thus actually more favorable in terms of regulation—body surface area-to-mass ratio.

DOI: 10.3238/arztebl.m2026.0026

Dr. med. Helmut Nocke

Institut für Physiologie, Magdeburg

References

1. Kriit HK, Herrmann A, Norris R, Rocklöv J, De Allegri M: Heat exposure and the risk of emergency hospitalization in Germany: Stratified analyses by age, sex, and diagnostic group. Dtsch Arztebl Int 2025; 122: 709–14.

2. Tsuzuki-Hayakawa K, Tochihara Y, Ohnaka T: Thermoregulation during heat exposure of young children compared to their mothers. Eur J Appl Physiol Occup Physiol 1995; 72: 12–7.

3. Taylor KM, Giersch GEW, Caldwell AR, Epstein Y, Charkoudian N: Relation of body surface area-to-mass ratio to risk of exertional heat stroke in healthy men and women. J Appl Physiol 2024; 136: 549–54.