Oxytocin, oestrogen and stress levels: How fatherhood changes the male brain

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A young father holding a newborn baby son at home. (Getty Images)
A young father holding a newborn baby son at home. (Getty Images)

Words by Gavin Newsham.

As a father to an as yet unspecified number of children, Prime Minister Boris Johnson should know only too well just what to expect as he, and his wife Carrie, get to grips dealing with their second child together, baby daughter Romy.

But while the effect on a woman’s brain after childbirth is well documented, the arrival of a new baby can also provoke a significant and sometimes startling neurological response in the male brain, especially in those areas of his brain that govern empathy, trust, affection and care.

Yes, even an old hand like Boris Johnson, 57, will be powerless to prevent it, as Dr Anna Machin, evolutionary anthropologist and author of The Life of Dad: The Making of a Modern Father, explains. 

“We used to say that being a mum was instinctive but dads had to learn how to parent,” she says. “We now know that both experience some of the same sort of biological changes – but as all parents know, there is much to learn.”

Pregnancy has been proven to alter a woman's brain - and it has an impact on expectant fathers, too. (Getty Images)
Pregnancy has been proven to alter a woman's brain - and it has an impact on expectant fathers, too. (Getty Images)

In 2016, a study by researchers at the Universitat Autonoma de Barcelona and Leiden University and published in Nature Neuroscience found that the outermost layer of the female brain, the grey matter, declined during pregnancy and after childbirth, often resulting in forgetfulness and heightened emotions. 

Significantly, though, it also revealed that there were no such changes in the male brain during this period.

That’s not to say it’s just business as usual for the new dad. Far from it. For example, oxytocin, the ‘love drug’ hormone and neurotransmitter, increases significantly whenever a man hugs or interacts with his new baby and his oestrogen levels will rise too. 

“In a dad’s case, he and his child get a peak in oxytocin from simply playing with each other,” explains Dr Machin.

That's not all. “Studies have also shown that if a man lives with his pregnant partner then their oxytocin levels synchronise,” she adds. “That acts to bring them closer, priming the parenting team to work closely together.”

And while the sleepless nights and a whole raft of new worries might begin to preoccupy the new father, the levels of the stress hormone cortisol actually decline sharply when they’re around their new addition (although they’ll doubtless rise sharply once the baby becomes a teenager).

Watch: Jamie Foxx regrets not making more time for his daughter

Men will even see an increase in prolactin, the hormone that also causes a mother’s breasts to grow during pregnancy and make milk after the baby is born and new dads will, at the same time, also experience a drop off in testosterone, the very hormone that makes a man a man, as their attention shifts from mating to parenting. 

Indeed, it’s been shown that men with low levels of testosterone tend to make better, more sensitive parents. “They’re better attuned to their child’s needs and quicker to be motivated to respond when they cry,” says Dr Machin.

One study, published in Hormones and Behavior journal in 2002, meanwhile, also suggested that the drop in testosterone could also be the result of a man’s emotional response to hearing their new baby cry.

The good news for partners, however, is that a man’s personality will also become less extrovert, meaning they prefer to spend more time at home with his new family, rather than pursuing the kind of social activities he might have enjoyed prior to the arrival of their child. 

“One aspect of you that will certainly undergo a major change during this period is your psychology, and particularly your identity and personality,” adds Dr Machin.

Research showed that the male brains change more when they are a parent of a girl than they do with a boy. (Getty Images)
Research showed that the male brains change more when they are a parent of a girl than they do with a boy. (Getty Images)

It’s changes like this that tend to mark dads out as the ‘fun parent’ but there’s also a marked difference in the way they can react to their new child, depending on whether it’s a boy or a girl. 

One 2017 study by Emory University in Atlanta, Georgia found that father’s brains change more when they are a parent of a girl than they do with a boy, prompting different responses when they interact with their new child and even the use of different language. “If the child cries out or asks for dad, fathers of daughters responded to that more than did fathers of sons,” said Jennifer Mascaro, one of the study’s lead researchers.

The research, published in the American Psychological Association’s journal Behavioral Neuroscience, also showed that dads with girls were frequently more responsive to their daughters’ needs and were much more open about their emotions than those with young sons; they even sang more often to them.

Whether or not Boris Johnson will be singing to Romy remains to be seen (or heard) but in the meantime, he will just have to get used to more sleepless nights at No 10 Downing Street – especially if there is, or isn’t, a party going on downstairs.

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