Bar Soap vs. Liquid Soap

Which Is Greener?

We all know that scrubbing our hands with soap and water is good for our own health, but how do different soaps stack up in terms of environmental health? A recent study on the environmental impacts of soaps and their associated packaging found that bar soaps have a lower environmental impact than liquid soaps in many important categories including carbon footprint, ecotoxicity, ozone depletion potential, and eutrophication potential. (1) This is due largely to the higher energy requirements of producing the raw materials and packaging for liquid soaps. From cradle to gate, liquid soaps require five times more energy for raw material production and nearly 20 times more energy for packaging production than bar soaps do. What’s more, the authors note, on a per-wash basis consumers use more than six times the amount of liquid soap (by weight) than bar soap.

However, before we declare bar soaps the environmental winner, it is important to note the study’s finding that bar soaps have a larger impact on land use than liquid soaps do. Bar soaps contain ingredients derived from vegetable oils, which come from farmed crops—and agriculture has a significant environmental impact on land.

In deciding which type of soap to buy, many people give more weight to carbon footprint and toxicity impacts than to land impacts. Arguably, however, impacts on land are just as important to our quality of life, and therefore one could justify choosing a liquid soap over a bar soap. Furthermore—although the study did not quantify water use over the entire life cycle of the soaps—we use more water when washing with bar soap than with liquid soap, the study noted.

The lesson here for the environmentally conscious shopper is that product selection is rarely a black-and-white issue. Deciding which product to buy often comes down to deciding which environmental impacts one is personally most interested in alleviating.

—David Tyler

1. Koehler, A. and C. Wildbolz. 2009. Environmental Science & Technology doi:10.1021/es901236f.

David Tyler is the Charles J. and M. Monteith Jacobs Professor of Chemistry at the University of Oregon.

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3 Comments

  • SeaKat June 11, 2013 at 3:32 pm

    Having made both kind of soap, I wonder if they are comparing apples & apples, or apples and something else. Liquid soap is made with the same vegetable oils as bar soap, and takes more energy to produce because you have to cook it longer – then you have to add more water back in and cook it some more.

    Reply

  • Debra June 13, 2013 at 9:37 am

    Not to mention the packaging. The bar soap I use is wrapped in coated paper (biodegradable) as opposed to the liquid soap’s plastic pump bottle which is only re-useable up to a point, then it breaks and goes to the landfill. I have not noticed any soap pump bottles labled as being made from biodegradable materials yet.

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  • Dave August 11, 2013 at 12:03 pm

    OK, this is incredibly frustrating. What fraction of the population cares enough to do a google search on “bar vs liquid soap”? Not many, but I’m one of them. I get this article. Great. But it doesn’t answer the question! OK, there are plusses and minuses. Fine. To make a decision, one needs to collapse all these issues into a grand scalar figure of merit, and choose the higher one. Of course there’s judgement in how to combine, say, CO2 vs land use. But that’s exactly what an expert should do! At least put out “here’s how I would weigh the factors, and thus my answer is X.”

    Or, better perhaps – if you want to weigh CO2 and land in such a way that liquid soap wins, then the same weighting applied in other situations would lead to choices you’d probably consider absurd (I can’t think of a good example now).

    So Mr. Professor – can you at least suggest an ethically valid way to combine these factors into a single number of badness / goodness and make the choice?

    Otherwise people will say, screw it, it’s complicated, I’ll just buy what I like or whatever is cheaper. Which maybe is just as well.

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