Did your baby run a marathon? Why so much sweat from simply napping and feeding?

Babies don’t sweat before they are born. They live in a liquid environment and mom controls their body temperature. So they don’t need to be able to sweat. Nobody knows exactly why, but sweat glands do not work until a baby is born. And then they work a lot.

In the first days, babies can only sweat on their foreheads even though they are born with sweat glands covering their entire body. The glands on the forehead are the only ones that function. So even though sweat glands cover the whole body, the nervous system hasn’t taken control of them yet. Over the first weeks of life, the rest of the sweat glands will start functioning. First babies will be able to sweat on their trunk, then on their arms and legs. Unless they are premature; preemies cannot sweat at all until after 37 weeks. So a baby born just 4 weeks early at 36 weeks doesn’t sweat. And they can’t shiver either, that’s why they have to be in an incubator. They aren’t able to control their body temperature the way we can.

The sweat glands on your hands and feet aren’t controlled by temperature at all, they only respond to emotional stress or pain, which is sort of creepy when you think about babies’ hands sweating. But scientists have measured baby palm sweat to determine if they are in pain when having their blood drawn, for example. Unfortunately, preemies palms don’t sweat either. As doctors, we are most interested in evaluating these fragile kiddos pain, but we can’t.

Preemies do have sweat glands (you can see them using a microscope) but they don’t work. Scientists actually discovered this by injecting baby’s skin with the body chemical that releases sweat from the glands. Even this radical intervention didn’t make preemies sweat. These same experiments showed that full-term newborns sweat from their heads, but not from the rest of their body. These experiments proved that full-term infants have fully functioning sweat glands, but their bodies just can’t control all of them yet.

Babies have 6 ½ times more sweat glands per square inch than adults, but they release a lot less sweat than adult glands do. As a baby grows they make a few more sweat glands, but mostly the glands they are born with just spread out as the skin grows.

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When the core body temperature rises a little bit, even just from just the excitement of getting to feed, and the accompanying increased metabolism, babies start sweating from their head. Their little bodies prefer to sweat from the head. As their body temperature rises and they need to get rid of even more body heat, they will eventually start sweating from the trunk, and from the arms and legs as a last resort. It is no coincidence that this is the same order that their nervous system developed control over their sweat glands.

This normal pattern of sweating is extremely important to notice. First, babies who have an abnormal brain don’t have normal heat-sensing neurons in their hypothalamus and they don’t sweat. So sweating is a sign of a normal functioning brain. Second, babies who are withdrawing from in utero cocaine exposure, even prematurely born ones, sweat all over their body because they had constant nervous system stimulation while they were developing and are born with overactive nervous system control of body temperature.

So your palms can stop sweating if your baby gets quite sweaty during naps or feeds, especially if it’s on their forehead and temples more than the rest of the body. Be reassured that your sweaty baby has a normal functioning brain and temperature regulation system.

 

References

Biology of sweat glands and their disorders. I. Normal sweat gland function. K. Sato, W.H. Kang, K. Saga, K.T. Sato.  Journal of the American Academy of Dermatology Volume 20, Issue 4, April 1989, Pages 537–563

Sweat function in babies with defects of central nervous system. Foster KG, Hey EN, O’Connell B. Arch Dis Child. 1971 Dec;46(250):879.

The Dermis. Nicholas Rutter. Seminars in Neonatology Volume 5, Issue 4, November 2000, Pages 297–302

The response of the sweat glands of the new-born baby to thermal stimuli and to intradermal acetylcholine. K. G. Foster, E. N. Hey, and G. Katz. J Physiol. Jul 1969; 203(1): 13–29.