Gender has a curious effect on pain perception, according to new research from Lund University in Sweden. In one study, it was discovered that male participants needed stronger pain stimulation to reach a required threshold when the scientist inflicting the pain was female. In another, male patients recovering from surgery tended to report less pain when questioned by a woman.
The researcher behind these findings is Anna Sellgren Engskov, a PhD candidate and medical doctor specializing in anesthesiology and intensive care. Supervised by Professor Jonas Åkeson, Sellgren Engskov set out to investigate the most common type of pain we experience, called nociceptive pain.
This is pain caused by damage to tissues within the body, visible or not, such as when we injure ourselves or undergo a surgical procedure. It’s mediated by two different types of nerve fibers that send signals to the brain at different speeds: the faster Aδ-fibers and slower C-fibers.
In the first of Sellgren Engskov’s experiments, healthy volunteers were subjected to pain caused by brief laser stimulation to their feet, but something emerged in the results that particularly surprised the researchers. It transpired that men taking part in the study required stronger stimulation to reach the required pain threshold when the person inflicting the pain was female.
The same pattern emerged in a follow-up study, where the participants inflicted pain on themselves using a button to trigger an electric shock. When the scientist supervising the experiment was female, both male and female participants needed stronger stimulation to feel pain. This is despite the fact that the scientists were dressed as neutrally as possible and stuck to an identical script regardless of gender.
These unexpected findings prompted Sellgren Engskov to take her research in a different direction, as she explains in her thesis: “The results on gender impact in the second study entailed me to test my hypothesis in a clinical setting and I designed a study on postoperative patients.”
This third study involved 245 patients at Skåne University Hospital in Malmö, all of whom were recovering from surgery. All patients were questioned about their postoperative pain by both a male and a female investigator, in a random order, with about 15 minutes between interviews.
“We were able to partially confirm our previous results here as well. Men, but not women, were in less pain when asked by a woman,” Sellgren Engskov said in a statement. “The differences were not that great, and probably have no significance at group level. But for the individual patient it can matter, especially given that the differences in pain were greatest when it hurt so much that the patients started asking for pain relief.”
It’s unclear why this difference was observed. The team speculates that one possible factor could be that women tend to have a greater capacity for empathy than men, and may express that in non-verbal ways – such as by smiling more or maintaining eye contact – that could affect patients’ experience of pain. There is some research to back up this assertion, as well as studies that have found better outcomes when patients are treated by or operated on by female medics, but it’s really too soon to say for sure.
However, the work does highlight the necessity of viewing pain in a more nuanced way. As well as the potential role of gender – both of the patient and the caregiver – the study also asked participants to describe their pain in their own words. The patients used different language to describe the faster, Aδ-driven pain compared with the slower, C-fiber pain. These quantitative descriptions could be useful when doctors are trying to quickly get a sense of how much pain patients are in.
“Perhaps the most exciting thing about Anna’s research project is that her own discoveries in connection with the first study – less pain with a female researcher – inspired her to want to investigate this more closely,” said Åkeson.
“Including the gender perspective when pain is evaluated can hopefully contribute to patients receiving even better care and pain treatment in the future.”
The research is detailed in Sellgren Engskov’s PhD thesis, which is due to be defended on November 17, 2023.