Premature babies are sensitised to pain by intensive care treatments they receive after birth, a study suggests.
Tests showed that pre-term infants that have spent at least 40 days in hospital feel pain more acutely than healthy new-borns.
Better pain-relief should be given to premature babies under intensive care to prevent them becoming pain-sensitive, said the researchers writing in the journal NeuroImage.
Pre-term babies can spend months in intensive care units undergoing painful procedures such as injections, tube feeding and blood tests.
Researchers carrying out the new study measured the brain activity of babies with an electroencephalogram (EEG) while they underwent routine heel lancing to draw blood samples.
The Medical Research Council-funded study showed that stronger EEG traces were seen for premature infants who had been in hospital for at least 40 days than for healthy non-hospitalised babies of the same age.
Brain activity seen when both sets of babies were gently touched on the heel showed no difference, suggesting that the sensitisation of pre-term babies is specific to pain.
This is important since the sense of touch is triggered by being held or cuddled.
It implies that premature babies can benefit from a mother's touch as much as normal infants.