Why does crying make babies hot?

Question

I have been looking into methods of preventing sudden infant death syndrome (SIDS) due to overheating during the current heatwave and from reading an article from MedicalNewsToday, Armstrong, (2020) states,

Crying can make a baby feel hot, causing them to sweat. This effect is more common when a baby cries very hard or for a long period. Some research [(Harpin & Rutter 1982)] suggests that babies may sweat on their palms and feet when they are upset. Parents and caregivers may notice this sweating even after a baby stops crying.

What is the cause of babies getting hot when crying while older children and adults don't?

References

Armstrong, M. (2020). What does it mean when a baby sweats? MedicalNewsToday https://www.medicalnewstoday.com/articles/baby-sweating

Harpin, V. A., & Rutter, N. (1982). Development of emotional sweating in the newborn infant. Archives of Disease in Childhood, 57(9), 691-695. http://doi.org/10.1136/adc.57.9.691

Answer 1

The neurobiology of crying in infants and adults is complex and poorly understood. As you might expect, direct physiologic studies of infants are lacking; however, some experiments have been performed in adults. Multiple investigators¹ have concluded that emotive crying is associated with increased sympathetic nervous system activity. ​

Experiments conducted many decades ago reveal that mediators of the sympathetic nervous system directly increase body temperature in mammals².

Moreover, the act of vocalizing the sounds of crying requires activation of the muscles of respiration. Muscle contraction intrinsically generates heat³.

Taken together, we can expect that the increase in sympathetic nervous system activity and heat generated by the muscles of respiration may physically increase the body temperature of a crying infant. This increase in body temperature can potentially make the infant "feel hot". In my opinion, the same physiologic mechanisms would (and do) apply to older children and adults.

One might argue that, depending on the age of the infant, cognition might not have sufficiently developed to the point where the infant can perceive the concept of hot, but that is probably a subject for another question.