Too Much Crying Can Damage Babies' Brains Prolonged distress releases too much cortisol, says Penelope Leach By Kevin Spak, Newser Staff Posted Apr 22, 2010 2:40 PM CDT 25 comments Comments Don't cry kid, you might hurt yourself. (Shutterstock) (Newser) – Letting your baby cry is not okay, at least if you believe parenting guru Penelope Leach. In her new book, Leach says recent brain research proves that letting young ones wail for prolonged periods puts them at risk of suffering brain damage. “It is not an opinion but a fact that it's potentially damaging to leave babies to cry,” she writes. “Now we know that, why risk it?” Crying is a signal of distress, she writes. and continual acute stress triggers the release of the hormone cortisol. Too much cortosol, from regular bouts of crying, can damage a developing brain, she says. But the issue is hardly settled. Lots of other child-rearing gurus say that letting your babies “cry down” is a good practice that helps them learn to fall sleep, and research published last month found that there were no ill effects to doing so, the Independent reports. But Leach pooh-poohs the idea of training babies to be self-reliant. A baby left to cry will eventually sleep, but only because “he's exhausted and has despaired of getting help,” she argues.