The Scientific Reason Why Air-Dried Laundry Smells so Good

I’m a big evangelist for hang-drying laundry. It’s the original form of solar energy, in which you use the sun to dry your clothes instead of an energy hungry dryer. Dryers account for something like 3% of all electricity usage (equivalent to all the solar panels currently installed) in the US, and hang-drying is a quick cheap solution to reduce your electricity usage so you can save that energy to power more crucial parts of your all-electric, decarbonized home.

Because I’m an evangelist, I help lead the annual Hang Dry for Climate Change week where a bunch of (OK, maybe more like a few) nerds, excited about the climate saving potential of hanging your undies outside, come together and celebrate the original form of solar energy (this year it goes from August 21 – 27, BTW).

During this year’s Hang Dry Week, we’re celebrating one reason to hang dry that people who grew up with dryers might never think about: air-dried laundry has an incredible smell. Those of us who sleep on sun-dried sheets can attest that the fresh, flowery aroma of clothing or bed sheets dried outside is incredible and something detergent companies try, but fail, to recreate. Everyone on planet Earth should (and most besides North Americans regularly do) experience this feeling.

A scientific study describes the reasons behind this phenomenon. Silvia Pugliese, a PhD student at the University of Copenhagen, studied what it is about hang-drying laundry outdoors that makes it smell so good. Silvia is Italian, which might help explain her interest in this topic. As an exchange student in that fabulous country, I witnessed how Italians make incredible use of the art of hang drying in every climate and season. In a country with the 8th largest economy in the world, 97% of the population doesn’t own a dryer.

Silvia’s research analyzed the scents of towels that were dried in the sun compared to towels dried in the shade or dried indoors away from the sun (note that the dryer wasn’t even tested or considered as an option). The team placed towels that were dried in these various methods in plastic bags and then analyzed their odors using gas chromatography coupled with mass spectrometry. The analysis showed that only when towels were dried outside in the sun were substances like carboxylic acids, aldehydes, and ketones detected. These substances are the same ones used in the perfume industry and have aromas like fruit, almonds, or citrus.

The chemistry is complex, but suffice to say that the presence of sunlight and water were necessary to “generate the odorous molecules.” These molecules then “bind with the cotton, which is a linear cellulose polymer, by hydrogen bonds,” and these hydrogen bonds are strong, meaning “the smell of fresh laundry is relatively long-lasting.”

The key finding is that you have to dry your laundry in sunlight to create the pleasant smells. So there you have it, yet another reason to hang dry. Want some free, natural perfume on your clothes and sheets that lasts for days? Try hang drying your clothes in the sun this summer. In the process you’ll save hundreds of kilowatt hours of electricity to power other machines in your all electric abode. And while you’re doing it, take a photo of your clothes harnessing the original form of solar energy and post it to #hangdryweek! Let’s create a movement to fight climate change with our laundry.

Read more about Silvia Pugliese’s study here and in the NY Times here