The absence of a mother's touch can severely affect the development of an infant's brain. Mary Carlson, psychologist and neuroscientist at the Havard Medical School, USA, says that the lack of physical touch increases levels of a critical stress hormone in a child's brain, making a baby ill-natured. This may lead to life long behavioural and physical problems. Children who do not receive regular reassuring physical contact experience levels of stress hormones far higher than normal. These can lead to impaired growth and development of both the brain and the body.