else, you'll make yourself sick.

Stress hormones may not only affect the competence of the immune system. We have found that they also act directly on bacteria to increase both their growth and virulence (ability to cause an infection). In fact, we and others have now shown that for dozens of infectious bacteria the presence of human stress hormones is a signal for the bacteria that they are inside a potential host, and that this host is stressed, its immune defences weakened, and the time is opportune to begin their attack. The stress hormones adrenaline and noradrenaline can turn blood that is normally very hostile to bacteria into a kind of bacterial tomato soup. Addition of these stress hormones to blood or serum will enable 10 bacteria to grow to 100 million cells in less than a day.

the news is not all bad, as intriguingly, we have also found that the same drugs that counter stress hormone effects in humans (for instance to lower blood pressure) can be used to stop bacteria responding to stress hormones.