When I was young we only had a bath once a week – the day, Friday, was known as ‘bath night’. In my great-aunt’s house a line was drawn in the bath to show where the hot water had to stop – it was about four inches from the bottom. Everyone in England smelt – of sweat and of unwashed hair.

But there are fashions in cleanliness and personal hygiene, as Virginia Smith points out in her immaculately researched book, Clean. No doubt in generations to come we will be just as amused by our obsessive attitudes to cleanliness in the twenty-first century as we are by those rules imposed by past generations.

Nature has made us a pretty grubby lot. We shed skin, hair and toenail clippings at the rate of between three to six ounces a day – that’s four tons in a lifetime. Around 80 per cent of the contents of a vacuum cleaner consists of human skin cells. And