Brace yourself for some bullshit science: a few months ago, lots of people announced the Northern line as the ‘dirtiest London Underground line’, thanks to a study by website Dr Ed, whose researchers swabbed 60 surfaces across ten tube lines. And they found an average of 1,647 colony forming units (CFU) of bacteria per 10cm! on the Northern line.
Unfortunately, that means approximately sod-all. According to Dr Adam Roberts from UCL's Department of Microbial Diseases, the amount of swabs taken ‘is so low I don’t think you can reliably say in general the Northern line is the most dirty line’. Plus, even if they hadn’t done a scientific investigation too brief to be of any use, what they would actually have proved is that the tube is surprisingly bacteria-free. ‘Those numbers are not really high. That’s not dirty,’ says Roberts. ‘There are billions of bacteria in a gram of soil.’ Moreover, he adds, ‘the tube is a difficult environment for bacteria to survive in – it’s very dry. There are far more dirty things that we surround ourselves with than the Underground.’
So there you go. Feel free to lick handrails on the tube: it won’t do you any harm.