Almost every household has at least one pair of shoes whose odour is impossible to ignore.
Multiply that by a family's worth of footwear, stack them on a rack, and you have a domestic design problem that's as pungent as it is universal.
Two Indian researchers decided this wasn't just about stink - it was about science.
They set out to study how foul-smelling shoes shape our experience of using a shoe rack, and in doing so, stepped into the hallowed - and hilarious - halls of the Ig Nobel Prize, a tongue-in-cheek award for silly but inventive scientific endeavour.
Vikash Kumar, 42, assistant professor of design at Shiv Nadar University outside Delhi, taught Sarthak Mittal, 29, during his undergraduate years. It was at the university that the two first hit upon the idea of studying smelly shoes.
Mr Mittal says he often noticed his hostel corridors were lined with shoes, often left outside twin-sharing rooms. The initial idea was simple: why not design a sleek, aesthetic shoe rack for students? But as they dug deeper, the real culprit emerged - it wasn't clutter but the foul smell that was driving the footwear outdoors.
"It wasn't about space or a lack of shoe racks - there was plenty of room. The problem was frequent sweating and the constant use of shoes that made them smelly," says Mr Mittal, who now works for a software company.
So the two embarked on a survey in the university hostels asking a truly human question: if our sneakers reek, doesn't that ruin the entire experience of using a shoe rack?
Their survey of 149 university students - 80% of them male - confirmed what most of us already know but rarely admit: more than half had felt embarrassed by their own shoes or someone else's stink, nearly all kept their footwear in racks at home, and hardly anyone had heard of existing deodorising products. Homegrown hacks - tea bags in shoes, sprinkling baking soda, spraying deodorant - weren't cutting it.
The two researchers then turned to science. The culprit, they knew from existing research, was Kytococcus sedentarius, a bacterium that thrives in sweaty shoes. Their experiments showed that a short blast of ultraviolet light killed the microbes and banished the stink.
"In India, almost every household has a shoe rack of one type or the other, and having a rack which keeps the shoes smell free would give a great experience," the authors noted in their paper.
They saw "smelly shoes as an opportunity for re-designing the traditional shoe rack for a better user experience".
The result? Not your average ergonomics paper - and just the kind of delightfully oddball idea: a prototype for a UVC light-equipped shoe rack that doesn't just store shoes but sterilises them. (UV covers a spectrum, but only the C band has germicidal properties.)
For the experiment, the researchers used shoes worn by university athletes, which had a pronounced odour. Because bacterial build-up is greatest near the toe, the UVC light was focused there.
The study measured odour levels against exposure time, and found that just 2–3 minutes of UVC treatment was sufficient to kill the bacteria and eliminate the foul smell. It was not simple: too much light meant too much heat which ended up burning the shoe rubber.
