A full-term infant has a three to four times greater risk of heat loss than an adult primarily because of which factor?

• A. Infant has a greater surface-to-body ratio
• B. Infant has a limited ability to sweat
• C. Thermoregulatory ability of the infant is immature
• D. Higher body fat

Answer: (A)

The main idea is that heat loss in newborns is driven by their large surface area relative to body mass. A baby’s small size means more skin surface per unit of heat to be retained, so heat is exchanged with the surroundings more quickly through convection, conduction, and evaporation. This high surface-area-to-volume ratio makes infants prone to rapid cooling even before their thermoregulation can adapt.

Thin skin and limited insulating fat in newborns amplify this effect, so they lose heat more readily than adults. While immature thermoregulation and limited sweating can hinder the ability to counteract cooling, they are not the primary physical reason for the increased heat loss risk. Higher body fat would actually reduce heat loss, so that option doesn’t fit.