London - Leaving babies to "cry it out" at night really may help them to soothe themselves.
Infants occasionally left to cry by their parents, instead of being immediately picked up and comforted, cry for slightly shorter periods by the age of 18 months, according to a study.
And its major finding is that encouraging babies to self-soothe probably does them no harm.
Children who were allowed to cry it out in their first six months were no more clingy or likely to have behavioural problems at the age of 18 months, despite previous suggestions that it could affect their development.
Researchers at the University of Warwick tracked 178 babies and their mothers over the children’s first year and a half.
They found that babies cried and fussed a little less often at three months old if they had been left to "cry it out" a few times after being born. If these babies were also often encouraged to self-soothe at three months old, they spent slightly less time fussing and crying at 18 months.
Experts say that letting babies cry it out a few times may be about setting boundaries, encouraging them to self-soothe, and not neglecting them as some anxious parents fear.
Study leader Professor Dieter Wolke, from Warwick’s department of psychology, said: "These results show parents don’t need to be anxious that it will harm their baby if they do not always immediately intervene as soon as a baby starts crying.
"Stepping in every time a baby cries can wear parents out, and put mothers at greater risk of stress and exhaustion. It may actually make it harder for them to be good, calm parents.
"Based on these results, we are advising parents to wait a few minutes before comforting their babies so they can learn to self-soothe and regulate."
The debate over crying babies has centred on whether leaving them alone makes them more insecure, or if responding to them encourages them to cry.
To see how being left to cry up until the age of six months affected children, their behaviour was observed at three and 18 months to judge things such as their attention span and communication skills.
Children were no different if they had been left to cry, and were not more upset, clingy or angry when researchers separated them from their mothers. The researchers had asked women if they left their children to self-soothe never, once, a few times or often after they were born and at three, six and 18 months.
They found older mothers in their 30s were less likely to leave their children crying at six months old, and higher-earning women were less keen to do this for three-month-old children.
Women who often let their children self-soothe were not worse mothers, but in fact less controlling and more sensitive to their children’s needs when observed playing with them at 18 months old.
The study, published in the Journal of Child Psychology and Psychiatry, found that around two-thirds of mothers never leave their children to cry it out at birth.
But more than half of study participants did it a few times when their child was six months old, and almost a third did it at 18 months. Dr Wolke added: "One of the first ways babies learn self-control is by falling asleep and controlling their crying."