Many people see stress as being inherently bad. It's not that simple though, since stress is a natural - and very valuable - reaction of the body. When we perceive a situation as threatening, our body goes on high alert. "The response is triggered in the brain," says Dr Ralf Suhr, chairman of the Berlin-based Health Literacy Foundation, a non-profit group aimed at enabling people to make informed health decisions. Chemical messengers called stress hormones - for example noradrenaline, adrenaline