Scientists asked 1,000 people to bury their underwear — what they found surprised them
A bizarre experiment used cotton underwear to reveal how active life is beneath the soil
It sounds more like a prank than a scientific experiment: Take a clean pair of cotton underwear, bury it in the ground, leave it there and then dig it up again.
But researchers in Switzerland had a serious reason for asking 1,000 people to do exactly that.
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Five years after volunteers buried more than 2,000 pairs of cotton underpants across Switzerland, scientists say the state of the underwear helped reveal striking differences in biological activity beneath gardens, farms, meadows and lawns.
The unusual experiment, called “Proof by Underpants”, has now produced a peer-reviewed study published in the journal Plants, People, Planet. Its central finding is straightforward: how land is used appears to be one of the strongest factors affecting how actively organisms break down material in soil.
Why underwear?
Cotton is made largely from cellulose, which microorganisms in soil can break down.
So researchers from the University of Zurich (UZH) and Swiss agricultural research centre Agroscope distributed organic cotton underwear to citizen scientists in 2021.
Participants buried 2,000 underpants and 12,000 tea bags at about 1,000 sites across Switzerland, following a standardised procedure. They later dug them up, photographed them and returned samples to researchers for analysis.
The principle was simple: the more cotton that disappeared, the greater the decomposition activity in that soil.
The researchers turned that into what they call an Underpants Index, comparing it with the established Tea Bag Index, another technique used to measure decomposition.
As Ars Technica reported in its coverage of the experiment, the underwear provided something the public could immediately see: some pairs came out relatively intact, while others had been reduced largely to waistbands and scraps of fabric.
Gardens ate the underwear fastest
Not all soils treated the underwear equally.
Private gardens showed the greatest decomposition, and also tended to contain high amounts of organic carbon and nutrients. Lawns recorded the lowest biological activity, while croplands and grasslands fell between the two.
Land use was the most important measured predictor of decomposition, ahead of individual chemical and environmental characteristics.
That does not mean, however, that underwear disappearing quickly automatically proves soil is “healthier”.
Researchers stressed that rapid decomposition can sometimes reflect very high nutrient levels. In gardens, for instance, unusually rapid breakdown could signal that too much fertiliser has been applied.
Temperature and moisture also matter: soil organisms generally become less active when conditions are very cold or dry.
There is an important limitation
The underwear test is better viewed as a simple indicator of biological activity, rather than a complete medical-style diagnosis of soil health.
The study's statistical models explained only 16.5 per cent of the variation in the Underpants Index, while models using the Tea Bag Index explained 21.5 per cent. The researchers acknowledged that this means several important factors affecting decomposition were probably not captured.
That distinction matters because soil health includes many characteristics beyond how quickly cotton decomposes, including nutrient balance, structure, biodiversity, water retention and chemistry.
The researchers describe buried underwear as a way to provide a “first impression” of soil condition rather than a replacement for detailed laboratory testing.
And hundreds of ordinary people became scientific authors
The project's scale would have been difficult to achieve using researchers alone.
Citizen scientists collected samples from regions across Switzerland, helping create what the University of Zurich describes as one of the country's most comprehensive datasets on soil life.
Around 240 of those volunteers are even listed as co-authors of the scientific paper.
The researchers now suggest that the Underpants Index could become an easy way to show people an ecosystem that usually remains invisible beneath their feet.
In other words, digging up a badly shredded pair of underwear might look like a laundry disaster.
For soil scientists, it can also be evidence that something underground has been very busy.
