Around ten million people a year in Britain suffer during the hayfever season, which peaks during the late spring and summer.

London - 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 US 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.

This allowed a part of the immune reaction called the inflammatory response to grow, leading to the symptoms of the cold, the journal Proceedings of the National Academy of Sciences reports.

Inflammation, which can show itself as redness, itchiness, swelling and pain, occurs when the immune system spots an infection and is vital in fending off disease.

However, when it persists, it raises the risk of many illnesses.

Researcher Professor Sheldon Cohen, of Carnegie Mellon University in Pennsylvania, said: “When under stress, cells of the immune system are unable to respond to hormonal control, and ... produce levels of inflammation that promote disease.” - Daily Mail