More online platforms are giving secondhand shopping a digital upgrade, rolling out features like livestream shopping and AI-powered search to make thrifting faster and more exciting.

Although choosing secondhand over new is often the more sustainable option, experts say it's not a license to overconsume. They warn that resale has its limits, since buying more than you need still fuels waste, and shopping online can add emissions from servers and shipping, thrifted or not.

Here's how industry experts and fashion-forward shoppers shop secondhand sustainably -- and how to find quality pieces that last while looking cool, too.

At eBay's secondhand runway shows in New York and London, models wore pre-loved designer pieces that guests could shop live. Secondhand items like those make up 40% of the company's sales, said Alexis Hoopes, eBay's vice president of fashion.

"One of our big priorities is making secondhand just as good as shopping in the primary market," she said.

ThredUp and The RealReal have reported record sales this year, signaling that the online resale market is growing quickly. Live-auction apps like Whatnot are giving shoppers more platforms to bid on used clothing.

Shoppers navigating growing online options with an eye toward sustainability can still end up buying more than they need.

"People who buy secondhand clothing were found to buy more clothing than people who don't," said Meital Peleg Mizrachi, a postdoctoral fellow at Yale University who researches textile waste. "Not only that, they tend to get rid of those clothes faster than other consumers. So they're ending up creating more textile waste because they're buying more and using that clothing for a shorter period of time."

Less than 20% of clothing donations to charities are resold in their stores, according to the Council for Textile Recycling. The rest is downcycled, exported -- often to countries in the Global South -- or ultimately discarded in landfills.

Online resale also generates emissions from shipping and packaging, and running massive e-commerce platforms consumes energy, all factors that need to be considered, said Alana James, a fashion professor at Northumbria University. But all of that pales in comparison to the environmental impact of producing a new garment, she said.

Experts say truly sustainable fashion requires breaking away from the fast-fashion mindset -- the constant pressure to "buy now" and the manufactured sense of scarcity that fuels overconsumption.

"Haul" culture -- the social media trend of showing off massive shopping sprees -- shows overconsumption in a new way, said Katrina Caspelich, communications director for Remake, an advocacy group for human rights and climate justice in fashion.

"Responsible secondhand shopping means choosing pieces you'll truly wear, investing in quality and resisting the pull of endless trend cycles," she said.

It can be difficult to determine quality when shopping online, but asking the seller about the garment's composition can help, said Wisdom Kaye, a menswear content creator.

Natural fabrics are a good place to start, said Caspelich.

"Look for silk, cotton, bamboo -- things that breathe and last -- versus synthetics like polyester or nylon," she said.

Shoppers should look for items that are lined and make note of the quality of the stitching, said Julian Carter, a menswear content creator.

Other secondhand buyers want to buy heftier clothing made before the mid-1990s, when more U.S. products were made without outsourced labor or a lot of cost-cutting, said Wesley Breed, a fashion history content creator.

From the year to the color, shoppers sifting through hundreds of thousands of search results online should be very specific about what they want, said Aimee Kelly, a fashion content creator.

"It helps you find the cooler pieces," she said. "And have patience -- look around, you're gonna find it."

Finding the right item is only the first step -- caring for it ensures it stays in circulation.

Stuff bags to maintain their shape, keep clothing in garment bags, and use muslin bags and lavender sprays to keep out moths that eat natural fabrics like silk, wool and fur, said Liana Satenstein, host of eBay's Endless Runway secondhand fashion show.

People can also wear clothes more between washes, spot-clean and air-dry clothes, and learn to sew.

"You'd be shocked how many people just toss a cardigan because a button fell off," Caspelich said.

Secondhand sustainability isn't just about keeping clothes out of landfills.

People who try to sell or give away their clothes should be mindful of where they're going, said Mizrachi, the Yale researcher.

"Try to give them to smaller community stores or shelters -- places that you know are happy to get those clothes," Mizrachi said.

Zara, H&M and other brands have launched recycling programs.

eBay recently partnered with British retailer Marks & Spencer for a take-back program that lets shoppers return items in-store to be resold on eBay.

But the most sustainable choice is simply buying less, Mizrachi said. The only way to make fashion companies change how they do business is to make overconsumption unprofitable -- which means buyers need to change their habits, she said.

"We can't purchase our way out of the climate crisis," Mizrachi said.

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