A lock of hair – it’s not just a keepsake.

For the first time, researchers at the Wisconsin National Primate Research Center have proven an infant’s delicate hairs could reveal the hormonal environment to which the fetus was exposed during gestation. Their methods have significant implications for several fields, from neonatology to psychology, social science to neurology.

“We had this ‘Aha!’ realization that we could use hair in newborns, because it starts growing one to two months before birth,” said Dr. Christopher Coe, UW–Madison professor of psychology and director of the Harlow Center for Biological Psychology.

While hair closest to the scalp reveals more recent information, moving down the shaft effectively transits an individual’s hormonal timeline. For the noninvasive study, researchers took small samples of hair from mother rhesus monkeys and their infants, cleaned them and pulverized the hairs into a fine powder. Scientists then read the hormonal signature using a new mass spectrometry method.

Researchers were particularly interested in hormone differences in infants born to younger, first-time mothers versus more experienced mothers. To test their question, they compared monkey mothers equivalent in age to 15-year-old humans to older monkeys. Scientists have long known maternal age plays a role in pregnancy and delivery outcomes, but evidence suggested something more.

Prior studies have shown high levels of cortisol can impair reflexes and attention and increase incidence of emotional and learning problems. In the monkey study, researchers found that cortisone, an inactive form of cortisol, was higher in young mothers and in their babies than in hair of the older mothers and their infants.

Both Coe and Amita Kapoor, first author of this study and a researcher at the Wisconsin National Primate Research Center, are particularly interested in how maternal age affects the “maleness” and “femaleness” of babies. Additionally, babies born to young mothers also had higher levels of estrone (a form of estrogen) and testosterone in their hair than did babies born to older mothers. Levels of both these hormones were surprisingly similar between male and female infants, raising questions about everything from the significance of birth order to stereotypical “boy” and “girl” behaviors in children.

Scientists studying humans are “really excited because [this method] is so noninvasive,” Kapoor said. Next up? Scientists interested in performing similar tests on humans are looking for answers to a longstanding question – how come human babies aren’t quite as hairy as other primates?

Reviewed August 2019

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Photo credit: Kathy West for the California National Primate Research Center