A few studies have shown that swearing actually can help reduce pain, but it doesn't work equally well for everyone. One of the best known investigations came from British researchers at Keele University, who set out to test whether swearing worsens pain, a popular hypothesis for many years. The Keele team recruited 67 undergraduates and asked them to make two lists of terms, one naming five words they might use after hitting themselves on the thumb with a hammer; the other list was of five words they might use to describe a table.
The students then put one of their hands into room temperature water for three minutes. Then they moved their hands to a container of cold water and were instructed to keep them there for as long as they could. They were asked either to repeat the first swear word on their list or to use one of the words they had listed to describe a table. The researchers timed how long the students were able to keep their hands in the cold water and asked them to rate the amount of pain this caused. The researchers also recorded the students' heart rates after they had submerged their hands in room temperature water as well as after they put them in the cold water.
The analysis of all this yielded the conclusion that swearing actually reduced the amount of pain the students said they felt when their hands were in the cold water, and enabled them to keep their hands submerged for 40 seconds longer than when the table-descriptive words were used. The swearing was also associated with increased heart rate.
And there was a difference between the men and women participants – the women had a greater reduction in pain perception and a greater increase in heart rate when swearing compared to the men. The researchers suggested that the effect of swearing in response to physical discomfort may be to initiate the "fight or flight" response, which speeds heart rate and reduces sensitivity to pain.
Another study, headed by the research team leader, psychologist Richard Stephens, used the same cold water and swear words routine. This time, the researchers found that the swearing worked less well to reduce pain for the student participants who reported cursing frequently, and noted that people with a propensity to express anger verbally tend to be more sensitive to both acute and chronic pain.
Incidentally, Stephens has been quoted as saying he decided to investigate the relationship between swearing and pain after hearing "the rather impressive selection of expletives" his wife used while giving birth to their second daughter in 2004.
Andrew Weil, M.D.
Richard Stephens, et al, "Swearing as a response to pain." NeuroReport 120:1056-1060. DOI: 10.1097/WNR.0b013e32832e64b1
Richard Stephens and Claudia Umland, "Swearing as a response to pain-effect of daily swearing frequency," Journal of Pain, doi: 10.1016/j.jpain.2011.09.004