The Case for Washing Clothes in Cold Water

If you wash most, if not all, of your clothes in cold water you might be surprised to find that you're in the minority.

Around 60 percent of Americans wash their clothes with warm water, explains George Dvorsky in a recent piece for io9. But, there two reasons that it might not be the best idea.

First, warm water needs to be heated and heat requires energy. Roughly 75 percent of the energy required to do a load of laundry goes into heating the water. Using cold water saves energy, putting less pressure on electricity grids. It can also save you some money. A recent estimate from Consumer Reports suggests that using a cold-water detergent and setting your machine to 60 degrees Fahrenheit (compared to 75 degrees Fahrenheit) can save you at least $60 annually in utilities.

Second, cold water can make your clothes last longer. Heat can break down dyes in the clothes and cause shrinkage. Thus, by washing clothes in cold water, colors last longer and clothes retain their size and shape. (The same argument can be made for line drying clothes instead of putting them in a really hot drier. Just ask my mom.)

Many opt to wash in warm or hot water because of the roles it can play in cleaning your clothes, writes Dvorsky. Heat typically makes chemical reactions go faster. This is where the type of detergent you use becomes important. Many powder detergents — and until recently most detergents in general — are made for warm water use. Chemicals called surfactants drive the cleaning process in heavy-duty detergents.

Like most soaps, surfactants are forever divided: One side of the molecule likes water, the other doesn't, as Richard Baguley and Colin McDonald explained earlier this year for CNET.  When surfactants form circular chains, they ensnare dirt particles. With the help of other chemicals that break stains down, the anti-water (or hydrophobic) end latches on to the dirt, while the water-friendly (or hydrophilic) end keeps everything afloat in the wash. Thus, particles of dirt, sweat and stains wash down the drain trapped in these tiny bubbles of soap. But, these chemicals don't work as quickly or efficiently in cold water.

Detergents designed for colder use get around this by a few different strategies, as Mary Johnson, a fabric scientist for Tide and Downy, told Dvorsky at io9. Using surfactant molecules that vary in length can create a more reactive environment. Special polymer molecules can boost the stain removal. Some enzymes can also help with stain removal. These proteins are based on those found in organisms living in cold ocean water, so for them, temperature is no issue.

Though tough stains might require some special detergent, most break up in cold water just fine. And the Earth will thank you for skipping that hot wash. 

Helen Thompson | | READ MORE

Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.