Sarah Ballantyne, a medical biophysicist turned author and lifestyle guru known as the Paleo Mom, has been an advocate of living in a more “stone age” way since reaching a healthy weight after adopting the Paleo diet. She, too, uses only water to wash, even though she is “at the gym sweating buckets six hours a week”. “I use coconut oil to shave and that’s it,” she says. “Over time, my skin has adjusted. I don’t smell.” She is working on a book about the human microbiome and is convinced her odour-free armpits are a sign that her skin microbiome is healthy.

Jackie Hong, a reporter in Yukon, north-west Canada, has eschewed soap in the shower for nine years. “I use my hands to scrub myself and get any grime off, but I’m sitting in court or at my desk most days, so it’s not like I’m getting bombarded with filth.” She was curious to go without soap after an artist told her that he hadn’t lathered up in 20 years. She says she saves time and money and needs “a lot less body lotion”.

“There’s nothing wrong with just rinsing,” says Sandy Skotnicki, a Toronto-based dermatologist and the author of the 2018 book Beyond Soap. “I’ve talked to people who haven’t used any kind of detergent in years and they’re perfectly fine.” She says that, since 1950, we have gone from bathing once a week to every day. “Has that changed our skin microbiome? I think the answer is yes. And has that caused a rise in inflammatory skin diseases? I think the answer is yes, but we don’t know.”