Scientists agree long-term stress can increase our risk of heart disease and cancer, plus make us more susceptible to infection.
But new research shows short bursts of stress could actually boost our immunity, help wounds heal and speed up surgery recovery.
Researchers from Stanford University in the US believe injecting patients who are about to undergo surgery with a dose of stress hormones could boost their immune system, according to a Daily Mail report.
In 2009, the researchers studied 57 patients who were about to have knee surgery to repair damaged cartilage. A few days before the operation, the researchers took blood samples to ascertain how many immune cells were circulating in the patients' systems.
Then, right before the surgery, they took another blood sample to identify which patients had the biggest increase in immune cells because they were stressed about the surgery.
Over the next year, they tracked the patients' recovery and found those who were most stressed before the surgery recovered quicker and had less pain than those who were more relaxed about the surgery.
Now, the Stanford team has gone one step further to pinpoint how stress boosts the immune system.
They took frequent blood tests from rats –– which increased their stress levels –– then monitored changes in the hormones norepinephrine, epinephrine and cortisol.
They discovered the rats' brains released the hormones in a specific order to send immune system cells to different body parts to defend them against attack.
Norepinephrine was released first and appeared to input cells into the bloodstream. Then epinephrine sent immune cells to the skin to help protect the body from injury. Lastly, cortisol was released. The whole process lasted about two hours.
The researchers said it appeared our bodies sent protective cells to areas that were most at risk of attack –– similar to dispatching troops in a war.
"Mother Nature gave us the fight-or-flight response to help us, not kill us," research leader Professor Firdaus Dhabhar told the Daily Mail.
But the magic is in short bouts of stress, as long-term stress actually suppresses the immune system.
"You don't want to keep your immune system on high alert at all times … but the evidence does suggest that putting oneself under short-term stress during procedures like vaccination or surgery can boost immune defences," Professor Dhabhar said.
"The key is that the stress really has to be short-term, lasting only for minutes or hours. It involves a rapid activation of the biological stress response followed by a rapid shutdown soon after the challenge is over."
Now the Stanford team is planning a study where they inject patients with stress hormones before they are vaccinated or operated on to see if it helps their recovery.
"If this is successful, it could provide a widely-applicable, relatively low-cost method for enhancing immune function," Professor Dhabar said.