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.
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.