Two separate studies, one from Northern Illinois University and one from the University of Pisa in Italy, researched hormone levels at S&M parties.
In the NIU study, those receiving stimulation got a boost in their levels of the stress hormone cortisol. The Pisa study showed a rise in testosterone among women who took part in S&M activities, which include spanking, bondage and flogging.
When the activities go well and are enjoyable, couples told researchers they felt closer to each other. However, the opposite was true of negative experiences with S&M.
"When sexual intercourse is consensual it is not stressful - even if it is extreme sex," Donatella Marazziti of the University of Pisa said.