Q. Dear Umbra,

Which soap is better for the environment, bar soap or body wash?

Jacob K.
Appleton, Wisc.

A. Dearest Jacob,

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The act of bathing, at first glance, seems pretty darn simple: Hop in the shower, suds up, feel clean, and be done with it. But as anyone who follows our adventures here at Ask Umbra knows, even the simplest daily activities usually sit atop a mess of complex issues, somewhat like an iceberg. It’s pretty fascinating to stick our heads underwater to suss out the true implications of our everyday choices — and in so doing, I hope, to think just a little more deeply and sustainably about life.

So let’s take a deep breath and put on our goggles to check out this particular iceberg. The first thing to know is that although both products help us scrub dirt and oils off our birthday suits, soap and body wash aren’t the same thing, strictly speaking. Soap is made from the combination of fats or oils, water, and an alkali (usually lye); body wash is usually a detergent, or a soap-like product containing extra chemicals called surfactants for added cleaning oomph. And while we usually think of soaps as solid bars and detergents as liquids, that’s not always true: True soaps can come in liquid form (like vegetable oil-based castile soap), and bar soaps can contain enough extra ingredients to count as synthetic detergents. Quick identification trick: If the label doesn’t actually say “soap,” it’s likely a detergent.

Now that we know the difference, which one to buy? Luckily for us, scientists have poured some research into answering this question, and we have a clear winner: bar soap.

Why? Well, for one, it requires a lot more energy to produce liquid soaps (er, detergents, technically) — about five times more. For two, liquid soaps can come with up to 20 times more packaging than a humble bar soap, which is often sold in minimalist cardboard boxes, sleeves, or sometimes just loose and wrapper-free. Liquid soap also contains a lot of water, which means those bulky plastic bottles are heavier and much less efficient to ship — so its carbon footprint from transportation is a lot larger. And once we finally have the bottles in our bathrooms, we tend to use much more of it: about seven times more per washing session, whether that’s because of overly generous pump dispensers or our own bad habits.

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And let’s not forget what’s actually in those pearlescent potions. Detergents are usually petroleum-based, to start (makes you feel a little dirty about soap, doesn’t it?). Manufacturers then pile on some questionable added chemicals, including parabens and other preservatives (suspected hormone disruptors), surfactants (some pollute our waterways), and phthalates (hormones again). Simple soaps look a lot purer in comparison.

This is not to say that bar soaps are completely environmentally benign, Jacob. Researchers have learned that we tend to use about 30 percent more warm water when washing up with a bar than with a liquid (though this study refers specifically to handwashing, so I’m not sure how it all shakes out in the shower). Soap’s vegetable-oil roots also mean it packs a bigger impact when it comes to land use. But when push comes to scrub, bar soap still wins as the greenest choice.

If this puts you in the market for a few soapy slabs, do take a look at the ever-helpful product ratings from our friends at the Environmental Working Group before you buy. Or, even better, shop around for locally made soaps to cut down even more on transportation-related emissions — these can often be found at neighborhood boutiques and farmers’ markets in all kinds of enticing flavors. You can even try making your own soap out of oils and a glycerin soap base; the internet is stuffed with how-tos.

I hope you’ve enjoyed peering at this soapy iceberg as much as I have, Jacob. Not only that, I’ve managed to make it this far without a single reference to how our icebergs are melting and we’re careening toward an apocalypse where we won’t even need soap. It is still the holiday season, after all, and I’m filled with the optimism of a brand-new year on the horizon.