Every day millions of bars of soap and half-used bottles of shampoo are discarded in hotel shower trays around the world; abandoned by guests who didn't stay long enough to use them up.
Many of these toiletries are scooped up by chambermaids, thrown into bin bags and sent off to landfill sites, which is a disaster for the environment and a social travesty given that many people around the world are going without proper sanitation.
The figures are startling: according to the World Health Organisation, millions of lives could be saved if the planet's poorest people had access to soap, a humble product that most of us take for granted.
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If only there was a way of diverting all those leftover toiletries to the people who need them most. Cue Shawn Seipler, a Florida-based entrepreneur who quit his high-profile job at a major tech company to recycle hotel toiletries. This unlikely career change began one night when Seipler found himself on the road with work.
"I called the front desk of the hotel and asked them what happened to the soap when I was done with it," he told Telegraph Travel. "Of course they said 'well we throw it away'."
So Seipler did some back-of-fag-packet calculations and concluded that millions of half-used bars of soap were being sent to landfill daily around the world. He was also aware that poor sanitation was killing millions of people in the developing world.
"I had a eureka moment," he said. So, in 2009, Seipler started collecting leftover toiletries from Florida's hotels, which he began recycling in a relative's garage in Orlando. Clean the World was born.
"We would sit around on upside down pickle buckets with potato peelers and scrape the outside of bars of soap to surface clean them," Seipler recalled. "We had meat grinders to grind down the soap, cookers to cook it into a paste and soap moulds, which we poured the paste into."
This laborious process is now fully automated (including the addition of an antibacterial agent, which kills any germs) and Clean the World has now distributed more than 40 million bars of soap to impoverished people in 115 countries.
The organisation has recycling centres in Orlando, Vegas, Montreal and Hong Kong and is currently looking to open a fifth in Europe (there are already collection centres in Birmingham and Hanover).
Clean the World has behemoths such as Hilton, Disney and IHG on its books. It charges them £1 per room per month and in return those companies get a chance to demonstrate some corporate social responsibility.
"We now have 303 hotels participating in the programme," Meera Thakkar, corporate communications manager at IHG, told Telegraph Travel.
"Clean the World has recycled 603,810lbs of soap and amenity waste from our hotels which has helped create more than 1.9 million bars of soap."
Most of the hotels taking part in the programme are based in North America, but Clean the World has started working with some European hotels. In fact London Heathrow Marriott recently enlisted the services of the organisation.
Other hotels have started introducing their own processes to minimise waste. The Hoxton, which has properties in Shoreditch, Holborn and Amsterdam, told Telegraph Travel that it has done away with individual toiletries.
"We've recently switched to using larger shampoo and conditioner dispensers in our rooms, which we refill to reduce waste," said Alice Tate, Hoxton's communications manager.
The Marriott has also introduced refillable dispensers at some properties, but guests shouldn't necessarily be waiting for hotels to make the first move. In fact there's something simple travellers can do with leftover toiletries that will leave them with clean consciences as well as bodies.
"Take them with you," said Seipler. "Use them at home or donate them to a homeless shelter."