Allergies. It seems like everyone has one, or two, or, to an extent, several more. These days you can’t go two steps without bumping into one. “Oops,” you say, “I’m sorry.” But the other person has already burst into a fit of sneezes and cold sores. Turns out they were allergic to apologies. Apalergies. You quickly run away to avoid prosecution. Unpleasant, right? Right! But what are allergies, exactly?

Allergies are basically the world’s way of saying it doesn't like you in very specific ways. The narrower the allergy, the pettier fate seems. For example, I'm allergic to fava beans and moth balls, which is the allergy equivalent of someone making fun of your shoelaces. I envy people with more general allergies, like cats or bread. And although they're more likely to encounter the thing they're allergic to, it's almost as if the commonness of it counterbalances the nuisance. They're more used to avoiding cats or bread and thus desensitised to how annoying it is. Especially if they're allergic to cats and bread, and doubly so if the allergy only activates when encountered together, which is increasingly likely what with the recent rise in popularity of feline toast. Compare that to old Fava-Bean McNaphthalene over here who rarely ever faces my allergens in the wild but when I do it's a horrible, harmful surprise. Like ankle splinters. Or being bitten by a duck.

Medically speaking, the concept of an allergy has been traced back to the early days of life. Bacterial cells which split and formed more bacterial cells needed some way of being put in their place. From that point on, all new life-forms had some kind of allergic reaction to their surrounding environment. When fish first stepped foot on land, their newly-formed walking appendages were not yet calloused enough to deal with the harsh coastal sand grits. Though this was less of an allergy and more just plain-and-simple stubbornness relating to their feet, something I have retained to this day (a stubbornness relating to other people’s feet).

Moving on, one out of three proto-monkeys found themselves mildly vomiting when eating early versions of the banana, which was mauve and donut-shaped. Ironically, as bananas themselves evolved into the modern yellow stick we know and love, they developed their own sets of allergies to certain movements in the earth’s atmosphere, which, even more ironically, would have rendered them perfectly safe for those poor proto-monkeys, had the latter creatures not died out due to malnutrition.

And so we move on to today, when all creatures on this bright weird rock have their own particular allergies, far-reaching and abstruse. Tonight on the train there was a passenger who was allergic to singing. If she even so much as encountered a single note she would break out in an unpleasant rash on the side of her leg. Even humming aroused welts, and she was occasionally known to twitch at whistles. Broadway was right out. (Probably for the best.) It didn't stop at people singing: parrots and even dolphins were a real and unfortunate threat. If this woman were Odysseus floating past the sirens she would still survive but end up with a nasty fever in addition to the rope burn. Understandably, she was wary of all sounds, especially those produced by the human mouth. To combat the phenomenon she was advised by an aural psychiatrist to focus her mind on noises that weren't singing if she ever encountered singing.

This particular night on the train it so happened that another passenger began a low, murmuring aria. At once the first passenger sprang up to silence the melody but the vocalising offender would not budge. Again she implored the stony-faced serenader to stop, mate, for the love of god, oh please stop. Mate. Mate. Mate. Stop it. Eventually the passenger looked up and with a frown faded out and resumed scrolling through their phone. But it was too late. There was already singing that had happened. Panicking as she could feel her elbows burning, she ran to the other end of the carriage and opened a whitegoods catalogue to imagine the clunky, emphatically amelodic whir of a washing machine. Another allergy attack averted. Phew.

Curiously, the case of the woman on the train was not an isolated incident. All over the world examples of sound-based psychosomatic reactions have been popping up with alarming frequency. In Tashkent a man will cough at the letter “t”, which is unfortunate on account of the name of his city. In Acapulco there is a woman whose eyes bleed when in proximity to gasps. And just last week I saw a baby who screamed at other screams – though I've been told that's just what babies do and they'll grow out of it naturally. I guess what I'm trying to say is: be careful with noises. You never know what they might do.

Do you have an allergy? Statistically yes. If so, let me know what it is – unless, of course, you are allergic to telling people about your allergies. In which case just keep it bottled up until you die. And if you don’t have any allergies, please let me know what allergies you don’t have. Sometimes these are the most interesting of all. Now if you’ll excuse me, I’m off to eat a slice of feline toast – which I am thankfully definitely not allergic to.