Add temperature control, or the lack thereof, to the list of a baby's vulnerabilities. Babies can't heat and cool themselves as well as adults can. They have fewer sweat glands, so they can't sweat as much.
The other means that adults use to heat and cool themselves through the skin is underdeveloped in babies. We've all seen ourselves flush when we exercise. When adults get hot, blood vessels in our dermis widen, moving blood from our core to our skin, where it can cool. When adults get cold, the vessels narrow to keep our core warm. Babies can't do this as well. This network of blood vessels doesn't fully grow and organize in babies until they're four months old [source: Dayan]. So, layer and ventilate to heat and cool your baby yourself.