Reid Reimers: Do your grandparents consistently harp on the importance of sorting your laundry by color?

Maybe you’ve had one or more knock-down drag-outs over whether you’re doing the laundry right. Or maybe they’ve instilled in you a fear of ruining all your white dress shirts thanks to just one red sock.

Boomers and millennials famously don’t see eye-to-eye on this issue. And it’s true that previous generations had to be diligent about sorting their lights from their darks. But the last 70 years of innovations in dyes, detergents, and fibers have made our light-colored clothes much safer than they used to be from errant red socks.

So here’s some clothing chemistry to take to your next textile-themed tussle with grandma.

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(0:45) Reid: There are three big things  to tackle when it comes to whether the dyes in your clothes will stay put. The dyes, how you’re washing your clothes, and the fabric itself. Unless you’re all in on the sad beige aesthetic, all the textiles in your home, from clothes to carpets, have been dyed. Dyes used to come only from natural  sources, like plants and minerals, or even crushed beetle shells and sea snail mucus.

But in 1856, a young chemist accidentally synthesized a bright purple dye. This monumental discovery spurred a broad interest in organic chemistry and the ability to make and sell custom chemicals. Soon other synthetic, designer dyes quickly hit the market.

Whether the dyes are natural or synthetic, they work the same way: by dunking fibers in a hot, stinky, colorful soup. These color baths allow the dye  molecules to bind to the fibers, and stabilizing those bonds is super important. Some dyes react directly with the fiber and form secure, covalent bonds.

Other dyes need help from a mordant, that is, metal ions that bind to both the dye and the fiber, securing their bond. A fabric’s ability to retain its dye when washed is called washfastness, and it’s a primary concern for the textiles industry. Companies know that consumers hate when their dyes run!

Reactive dyes, the ones that form super solid covalent bonds, became popular in the 1950s, due to their incredible washfastness. And mordanting chemistry has also gradually improved over the decades, leading to a winder range of washfast dyes. All of which contributes to far less of an indigo tinge in your load when you wash a new pair of blue jeans.

Which leads us to detergents. But first, we have to buy laundry detergent like anybody else, so let’s go to this quick break. This SciShow video is supported by Sendacake.com: the unique gifting experience that levels up any celebration.

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I know Send A Cake is meant to be sent to someone you’re celebrating, but if you live in the US, you might just want to send this to yourself. If you know a mom anywhere in the US, you can send them this memorable Mother’s Day gift for 10% off using the code SCISHOW at Sendacake.com. Laundry detergents have also vastly improved in the past 50-ish years.

Detergents have molecules called surfactants, which specialize in bonding to both oily grime and water, so that the surfactant-trapped dirt washes away with water. These molecules depend on getting deep into the fibers of your clothes, sticking to the dirt, and subsequently getting  flushed out by the rinse cycle. Big Laundry likes to keep their exact detergent recipes secret, so we won’t be able to talk  about the exact chemistry here.

But we do know there’s been huge innovations in recent decades. Compared to harsh, historical cleaning agents, modern detergents are just way better at binding to dirt without stripping other molecules – like dyes – from the fibers. And by the 1970s, most detergents included enzymes: proteins that break down the stuff that stains your clothes or makes you stinky.

And there’s a neat trick  here – having more efficient enzymes means detergents  can use gentler surfactants, which can be pretty harsh sometimes. Cutting down on those surfactants  results in fewer harsh chemicals in laundry wastewater, and a smaller environmental impact on our waterways. And your clothes still get clean.

But the most important factor here is that detergents perform way better in cold water than they used to. Since dyes are set at high temperatures, washing in hot water can… well, un-set them. And 50 years ago, clothes had  to be washed in hot water, about 60° Celsius or 140° Fahrenheit, to remove the most dirt.

That strains the bonds between dyes and fibers, and also uses a lot of energy just to heat the water. But after 2005, most laundry detergents on the market work just as well in cold water as in hot! Since this is a relatively recent shift, this might be the biggest point of contention between you and your grandma.

Traditional advice recommended washing light-colored clothes and bedding in hot water to remove the most dirt, while washing dark-colored clothes in cold water to prevent running dye. Now that detergents work well at the optimal temperature for washfastness, separating seems much less of a concern. Fibers are the final factor in this debate.

Historically, all textiles were made from plant- or animal-based fibers. But now, synthetic fibers are everywhere. By synthetic, we mean derived from petrochemicals… which is to say, plastic.

As of 2022, synthetic fibers account for about 65% of the fibers in our textiles. Synthetic fibers were discovered, slash invented, between the 1930s and 1960s. And by the 1980s, polyester and nylon in particular were HUGE.

Just like many hairstyles of the era. By the 1990s, synthetic fibers comprised the largest percentage of fibers by volume. Polyester remains the most popular of the synthetics, accounting for an estimated 54% of global fiber production in 2022.

In fact most textiles are now a blend of synthetic and plant- or animal-based fibers. Because of the molecular structure of synthetic fibers, their dyeing process can’t rely on the reactive methods that result in covalent bonds. Rather, polyesters are colored with disperse dyes.

In this method, dye particles are milled to be about 1 micrometer across—small enough to get trapped and tangled within the fibers. These dyes are water-insoluble, meaning they don’t bind to water at all and therefore cannot easily be washed out. That means synthetic fabrics demonstrate incredible washfastness.

Synthetic fibers are stretchier, cheaper, and more colorfast than naturally-derived fibers. They can be moisture wicking, water repelling, flame retardant, and electrically conductive. They sound like miracle fabrics!

But despite these amazing applications, there’s no free lunch. Because every time a synthetic fabric is laundered, it sheds a huge amount of fiber fragments, aka microplastics. Many of which will end up in our  waterways and eventually the ocean.

In fact, the washing of synthetic fabrics is responsible for an estimated 35% of global microplastics pollution. So, you know, pros and cons. These simultaneous advancements across dyeing, detergents, and fabrics means that these days we don’t have to worry much about our dyes running in the wash.

Top laundry scientists do still recommend sorting your lights and darks, just to be safe, and to wash in cold water to prevent color bleeding. If you get something new, it’s also worth pre-washing it alone or with like colors, to rinse out the remnants of the dyeing process. Armed with these facts, you can make an informed decision to either go the safe route, or to chuck it all in and call it a day.

Even with these convenient innovations, the textiles industry is still a major source of water pollution and industrial waste. Synthetic fabrics in particular have accelerated cycles of textile overconsumption and microplastics pollution. Regulations in the 1960s successfully cut down on laundry soap runoff in domestic waterways.

And there’s tons of ongoing research in natural dyes and fibers, with the goal of reducing the environmental impact of our clothes. So hopefully the next revolution in textiles will be to clean up production processes with more sustainable methods… while still not turning all your other clothes pink.

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