They say that boys who have been circumcised have their pain response enhanced - an effect that can last for several months after the procedure has been carried out. That meanspain relief should be given to the babies before circumcision to save them from pain later.
Curious as to why boys appear to experience more pain, Dr Gideon Koren of the Hospital for Sick Children, Ontario, set up an experiment to measure the distress caused by the needle.
The boys, aged four to six months, were having routine diphtheria-whooping cough-tetanus injections. Some were also given an injection for meningitis. Half the babies had a local anaesthetic cream rubbed on their thighs half an hour before the injections. All their responses were recorded on video and assessed by an impartial observer.
Dr Koren says in the Lancet that the circumcised boys, who made up 71 per cent of the total, overall had more pain. "Male circumcision is the most common neonatal surgical procedure. It causes intense pain and measurable changes in behaviour that last upto a day.
"We found that circumcision was associated with increased infant pain response. Circumcised boys had significantly longer crying bouts and higher pain scores."
Pain was measured by evaluation of the expression on the baby's face, his movements and his crying.
Dr Koren says that although his observations are speculative, given the small number of babies in the test, pain relief should be given routinely to those to be circumcised.