One final point is that there is a curious parallel with Norwegian health folklore, which says that women are more likely to develop cystitis when the weather is cold. Researchers found that cooling people’s feet did seem to activate cystitis in some women, suggesting that the same process might be occurring in the urinary tract, as in the blood vessels of the nose and throat.
So there might well have been some truth in my grandmother’s advice not to go out with wet hair. It will not give you a cold, as she said, but it might trigger one. In the meantime, until more research is carried out I think I will dry my hair before I go outside.
You can hear more Medical Myths on Health Check on the BBC World Service.
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