Why being stressed can wreak havoc with your immune system

As many of us know, stress can leave you feeling run down. Now scientists think they can explain why.
A study has shown how long-term stress plays havoc with the immune system, raising the odds of catching a cold. The same process could also explain  the role of traumatic events in raising the odds of illnesses from heart disease to depression. Scientists in the U.S. questioned 176 men and women about difficult experiences they had been through in the past 12 months.
Drops of the common cold virus were then dripped into their nose and scientists checked if they caught the germ. Those who had been under stress were twice as likely to develop a cold.
Importantly, tests showed their immune systems had become less sensitive to cortisol, a stress hormone which dampens the immune system.

Source  - Daily Mail