Two new studies by researchers in Japan and Germany found that pain is a complicated mix of responses in the mind and in the body.
And feeling sad or watching while receiving an injection, they said, could make pain an even more unpleasant experience, the BBC reported.
In the first study, a team at Hiroshima University showed pictures of sad, happy and emotionless faces to 19 people in the experiment. The pictures are supposed to provoke a similar emotional response in the person taking part.
At the same time, the participants were zapped in the arm with an electrical current. The painful jolt was the same strength each time, however, the people in the study reported higher levels of pain when looking at sad faces.
"Our results provide evidence that people tend to show higher pain sensitivities when they are feeling sad, and that emotional context is an important factor for understanding pain in human beings," the team wrote in The Journal of Pain.
A separate investigation by a team at University Medical Center Hamberg-Eppendorf in Germany tried altering pain in a different way.
They replaced 25 people's left hand with a virtual one. A video of a hand was played on a screen and the participant's hand was placed underneath the screen so that it appeared as though the image was really their own hand.
The video would show either just the hand, the hand being pricked by a needle or being poked with a cotton bud.
An electrical jolt, either painful or non-painful, was given at the same time as the prick or the poke.
The researchers, writing in the Pain Journal, said: "Both painful and non-painful electrical stimuli were perceived as more unpleasant when participants viewed a needle prick, compared to when they viewed [cotton bud] touch or hand alone.
"This finding provides empirical evidence in favour of the common advice not to look at the needle prick when receiving an injection." PTI SKP AKJ
