Do you have a cold? Thought so. If not you, then a workmate. Or the man beside you on the train, who looked like he was going to be able to hold it in, but has just - atchoo! - sneezed all over the crossword. Britain has caught cold. Or is it flu?

Most people have only a blurry idea of the difference. They regard a cold and flu as two extremes of a spectrum of feeling sneezy and sick with self-pity. It tends to conjugate as follows: I have flu, you have a cold, he is a malingerer. It is true that the flu season has started much earlier this year, hitting levels not usually seen until January or February (see opposite page). But even scientists are not sure why colds and flu are more common in winter in the first place, although they are pretty sure that it has little to do with it being colder (people who work in Antarctic research stations rarely catch colds, and the 1918-19 flu pandemic reached its peak in the late spring).

Cold seems to promote colds only in the indirect sense that people stay indoors more in winter, and more people in a confined space means that viruses get transmitted more aggressively. Children catch more colds than adults because they mingle with other children at nurseries and schools. They then pass the virus on to their families. By contrast, those older than 60 tend to catch fewer than one cold a year.

So as you sneeze, wheeze, cough and nurse a throat as raw as a carpenter's rasp, you are just one more hapless victim of this winter's curse: a triple assault by three strains of cold, stomach bug and flu all noted for striking early in the flu season. But having arrived earlier, this year's viruses may leave sooner too. So that's the good news: your flu isn't for life, it's just for Christmas.