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Why Do Babies Curl Their Hands Into Fists? Experts Explain The Science Behind It

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Babies are the cutest little creatures on earth, and some of their quirks, like crossing their eyes or balling their fists, just add to the overall appeal. But sometimes I have to wonder what causes these little things to happen. Like why do babies curl their hands into fists like tiny boxers?

It turns out that there is a developmental reason that babies always look like they're ready. Megan Shimkaveg, MD, pediatrician at the University of Maryland St. Joseph Medical Center tells Romper, "Babies make fists because they have a reflex known as the palmar grasp. You can elicit it by gently pushing on the palm of a baby’s hand with your thumb, and he or she will curl the fingers of that hand around it in response." StatPearls noted that the palmar grasp "is a primitive, prehensile, involuntary response to a mechanical stimulus present in a newborn." It has to do with the developing brain and its system of nerves and fibers including the spine.

Pediatrician Dr. Lisa Lewis tells Romper, "Babies begin using this involuntary reflex in the womb, during the second trimester of pregnancy. They continue folding their fingers into a fist after birth, and their hands begin to unfurl after 3 to 4 months." And anyone who has had the unfortunate experience of having their long hair caught up in the palmar grasp of a baby knows just how strong of a grip those little humans can manage.

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"By age 4 months, most babies will discover they can actually use their hands to bat at objects," Lewis says. Checking for the palmar grasp — watching babies curl their hands into fists — in newborns and again at 6 months is a part of typical pediatric visits. That's because, as StatPearls noted, a weak grasp in early infancy, or a prolonged palmar grasp that occurs after 6 months, might indicate an underlying abnormality.

For most babies, it's just a cute thing that they do when they're fresh out of the womb. (So long as they don't get a fistful of your hair, then it's not as cute.)

Experts:

Megan Shimkaveg, MD, pediatrician at the University of Maryland St. Joseph Medical Center

Dr. Lisa Lewis, pediatrician