Premature or underweight babies kept in an incubator away from the touch of their mothers for their first few weeks suffer physical and emotional problems that can damage their lives, a 20-year study suggests. Israeli researchers presented their findings after following the progress of 146 pre-term babies – half of whom were separated from their mothers and half of whom received kangaroo care, in which they were allowed an hour a day of skin-on-skin contact for 14 days – since the late 1990s. By the age of 20, those cut off in incubators in their first few weeks had shown problems in regulating their emotions and had poorer self-control. They also had weaker immune systems, struggled with sleep and were stressed more easily. Tests showed that they had almost three times the level of the stress hormone cortisol compared to the kangaroo care babies. Researchers said the first few weeks of a premature baby’s birth set the stage for its social, mental and physical development and being close to the warmth, smell, microbiome and heartbeat of their mother was vital. "In the children who are now 20, you see a marked difference in how they are behaving,” said study leader Dr Ruth Feldman, of the Interdisciplinary Centre Herzliya. “All these kids are doing fine, and they graduated from high school, but these issues are under the skin. They [babies who had been in incubators] will do less well, will have greater stress and will be less able to regulate their anger, and there are issues with social maturity and empathy. “It seems the brain really has this critical window of opportunity and it sets the stage for problems in later adulthood.” Around 60,000 babies are born prematurely in Britain each year. A premature birth is defined as being before 37 weeks, with a full-term pregnancy lasting for around 40 weeks. Although guidelines from the National Institute for Health and Care Excellence recommend skin-on-skin contact they do not officially recommend kangaroo care, which not all NHS trusts use. Kangaroo care, in which an unclothed baby is placed directly on the mother"s chest, is the only way a premature infant can be outside the incubator because the heat is regulated by the mother. Researchers believe being close to the mother "tunes" the brain of the baby, creating synchrony and helping boost empathy. “It"s not just touch, it"s the entire envelope of the mother’s body and it has many components – the mother"s smell, the mother"s heart rhythms, the mother"s movement, and we"re beginning to look at the transfer of the microbiome," Dr Feldman said. Kangaroo care was developed in the 1990s, with doctors having believed before then that babies were too ill to be removed from an incubator if born early. “All these premature infants were neurologically intact, but the difficulties in cognitive flexibility are important,” Dr Feldman said. “Life now requires so much flexibility, the ability to evaluate multiple options, the ability to persist, the ability to change and regulate emotions. If you are lacking that in such a competitive world, then you are starting at a disadvantage. "It could mean they struggle to reach their full potential, and life for them will be harder. Higher stress and inflammatory responses spell a lot of risk in adulthood and old age, bringing both physical and mental disorders, so there is something about the provision of maternal bodily contact that sets the child on a different trajectory.” Andrew Shennan, a professor of obstetrics at King’s College London, said: "Kangaroo care is known to be beneficial to babies, and it is plausible that this care could benefit brain development. "Around the time of birth, especially in premature babies, inflammation is known to affect the brain and this can be influenced by stress hormones. A calming environment associated with kangaroo care will reduce these stress hormones, which could explain the results seen over the impressive 20-year follow-up, although more research is needed." Researchers believe the problems shown in the study may also impact full-term children who had been kept away from their mothers because they were underweight or sick at birth. They now want to follow the progress of the people who they have tracked since they were children in the 1990s to see what effects may be passed on to their own children. The findings were presented at the American Association for the Advancement of Science conference in Seattle.