Cedars-Sinai Medical Center performed a study that shows a single massage produced measurable changes in the immune system & endocrine system of healthy adults. For example, Swedish massage caused sizeable decreases in arginine vasopressin, a hormone that contributes to aggressive behavior, & small decreases in the stress hormone cortisol. The Swedish massage participants also had an increase in lymphocytes, cells that help the immune system defend the body from harmful substances.