Q: What’s the most sustainable way to wash your hands or lather up in the shower?
A: In general, the greenest option is an old-school bar of soap made from plant oil or animal fat and lye, without many extra ingredients. Simple bar soap cuts greenhouse emissions by about a third compared with liquid soap, according to a study from the Institute of Environmental Engineering at the Swiss university ETH Zurich.
“Soap is a natural product, it’s sustainable, and it’s been used for a long time,” said Tony O’Lenick, president of the Society of Cosmetic Chemists, a professional association for the scientists who concoct recipes for beauty products. The downside: “That kind of soap dries skin out,” he added.
That’s why many people have turned to liquid hand soap and body wash, which have seized about half the American soap market since their introduction in the ‘70s and ‘80s, according to sales data from Mintel, a market research company. Liquid soaps and body wash typically come with extra ingredients to moisturize skin, and many brands advertise the skin care benefits of their products.
“A lot of those new claims have mostly been tacked onto liquid formats, particularly liquid body wash, which has kind of left bar soap behind,” said Joan Li, a senior beauty and personal care analyst at Mintel.
But lately, the soap market has gotten a lot more complicated: Many bars of soap – looking to ditch their reputation as drying – now contain the same artificial, petroleum-based ingredients and moisturizing additives as liquid soaps. And some liquid soap – in a bid to market itself as eco-friendly – is now made from the simple, natural ingredients found in old school bar soap.
If you want to cut through the noise and pick the greenest option, according to O’Lenick, you should think about ingredients, packaging and the differences in how you scrub with bars vs. liquid soap.
Ingredients
All soap cleans dirt and oils from our skin using molecules called surfactants, which help water pick up grime and wash it away. But there are two ways of creating surfactants.
The old-school way is to combine fat and an alkali such as lye – the basic ingredients of soap for centuries. But around the 1940s, O’Lenick says, cosmetic companies found a cheap way to make surfactants out of petroleum. Technically, he says, chemists don’t call these products “soap” – they are “detergents.”
Although they clean more or less the same way, soaps and detergents have a couple of key differences: Soaps tend to be more alkaline than detergents, which changes the chemistry of your skin and leaves it feeling drier. But detergents are made from drilling and refining oil, so they tend to be worse for the environment. Making detergents uses five times as much energy and produces about 10 times as many greenhouse emissions as making simple soap, according to the Swiss researchers.
To understand whether you’re buying a natural soap or a synthetic detergent, you have to look at the label, O’Lenick said. Most products – even most bars of soap – are made from detergents, which contain ingredients such as sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES).
True soaps made from animal fat or plant oil as well as lye may also contain additives, such as glycerin, scents and essential oils.
Packaging and transportation
Ingredients aside, bar soap has a clear advantage over liquid soap when it comes to packaging and transportation.
Bar soap typically comes with minimal packaging – a cardboard box, paper or nothing at all – which is often easy to recycle. Soap bars also sometimes come in plastic wrap, but it’s generally less material than liquid soap, which comes in thicker plastic containers that sometimes contain pumps that are hard to recycle. Packaging liquid soap is 19 times as energy-intensive as packaging bar soap, according to the Swiss study.
Plus, liquid soap is mostly water, which means the majority of what gets shipped around the world from a factory to your doorstep is something you could get from your faucet. Bar soap is pure, concentrated cleaning product; you pay only for the soap, and you add water when it’s time to lather up. Distributing liquid soap creates nearly eight times as many carbon emissions as an equivalent amount of bar soap, according to the Swiss study.
Scrub time
One big advantage for liquid soap over bar soap is that people typically spend less time lathering, which means they don’t use as much warm water, according to the Swiss study – although it made that comparison only for handwashing, not showering.
Bar soap scrubbers typically use about 40% more water, according to the study. That’s by far the biggest source of environmental harm from using bar soap – but it’s not enough of an impact to make bar soap worse overall than liquid soap, according to the study.
Does it make much difference?
But whether your soap is bar or liquid, natural or synthetic, it’s not going to be a huge part of your carbon footprint. In the worst case, washing your hands creates 15 grams of carbon emissions, according to the study – the equivalent of charging your phone one time, or driving a car 200 feet. We’re not judging you for the soap that you use.
But, collectively, that can add up as billions of people wash their hands or bathe hundreds or thousands of times a year. If you’re so inclined, it makes sense to switch to a more eco-friendly product. Just understand that there may be a trade-off between sustainability and comfort.
“The consumer has to decide: Are they serious about where their soap comes from, whether it’s synthetic or natural? And do they like the feel of the product?” O’Lenick said. “You could have the most sustainable soap in the world, but if it doesn’t feel good, you’re not going to sell [more than] one bar to everybody that comes around.”
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