Donating your old, unwanted clothes is a great way to give back to your community while cleaning out your closet. It's a satisfying feeling knowing that you've made a positive impact, providing people with clothes who might not otherwise be able to afford them.

When you drop off that bag of old clothes at your local Goodwill, though, there's probably one thing you aren't thinking about: those clothes don't always go to those who need them — or to anyone at all. Believe it or not, a large portion of the clothing you donate ends up in landfills.

The fashion cycle moves too fast

Fast fashion cycles have become the norm. Not only do rapid cycles in fashion make keeping up with clothing trends difficult, but they inadvertently create an environmental crisis — ever-changing fashion cycles mean more clothes are being trashed than ever before.

If you're donating your clothes or taking them to a consignment shop, often times the clothing won't be accepted due to flaws. And in the case of consignment shops, if the clothing is no longer in style, then there's little to no resale value.

There's also the issue of the disparity between clothes that are donated and the amount of used clothes that are actually purchased. Only 28 percent of people donate used clothing, and a mere 7 percent of people purchase used clothing, according to Savers 2018 State of Reuse Report.

With that kind of math, it's not so surprising that landfills — and not other people's closets — that become the final destination for the clothes.

Excess clothing and its environmental impact

By 2019, it's projected that Americans will have generated 35.4 billion pounds of textile waste. Srdjan Randjelovic/Shutterstock

When you look at how much clothing is wasted, the numbers are staggering:

• As of 2014, Americans buy five times more clothing than they did in 1980, reports The Atlantic.

• The Environmental Protection Agency (EPA) estimated that in 2015, textile waste (mainly discarded clothing, but also footwear, carpets, sheets, towels, and tires) accounted for 7.6 percent of all municipal solid waste in landfills; that's 10.5 million tons of textile waste.

• 40 percent more textiles were thrown away by Americans from 1999 to 2009, reports the Council for Textile Recycling. That means that in 1999, 18.2 billion pounds of textiles were trashed, and the number of textiles wasted rose to 25.46 billion pounds by 2009. By 2019, it's projected that Americans will have generated 35.4 billion pounds of textile waste.

• Over roughly the past 20 years, the amount of clothes that Americans have disposed of has doubled from 7 million to 14 million tons (somewhere in the ballpark of 80 pounds per person), and in 2012, the EPA reported that 84 percent of unwanted garments made their way to landfills and incinerators, says Newsweek.

• In New York City alone 400 million pounds of clothes are wasted every year, according to Popular Science.

All this clothing in landfills and incinerators just translates to more waste that pollutes the environment; this is true whether the fibers are natural or synthetic.

While fibers like cotton, linen, and silk are natural, they don't degrade in the same way as natural materials like food.

"Natural fibers go through a lot of unnatural processes on their way to becoming clothing," Jason Kirby, CEO of the Sustainable Apparel Coalition told Newsweek. "They've been bleached, dyed, printed on, [and] scoured in chemical baths." When clothing that's received such heavy chemical treatment is burned in incinerators, harmful toxins are released into the air.

Synthetic fibers such as nylon, polyester and acrylic are made from petroleum (a type of plastic), and plastic can take up to 500 years to biodegrade, according to Slate.

As far as clothing that's actually donated and not purely wasted, only close to 20 percent of Americans' clothing that goes to consignment shops and thrift stores are sold to consumers. In 2014, 11 percent of Goodwill donations were seen as unfit for sale and ended up in landfills. That 11 percent translates to about 22 million pounds, according to Fashionista.

The remainder of garments that aren't thrown away or can't be sold are baled up and shipped overseas to markets in sub-Saharan Africa, which can sometimes be considered problematic since it puts local textile workers out of work, reports BBC.

Playing your part

Do you really need another white shirt? Buying less in the first place is a great place to start. stock around me/Shutterstock

It would be unrealistic to expect fashion cycles to slow down anytime soon. More and more clothes will be manufactured, they'll continue to be purchased, and in many cases they will one day be thrown away. And while more people may jump on the secondhand clothes bandwagon, it seems unrealistic to think this will become a worldwide trend.

This is not to say that all is hopeless. If you don't foresee secondhand clothing becoming a major part of your wardrobe, there are plenty of textile recycling services out there.

There's American Textile Recycling Service, which provide recycling bins for various textiles all throughout the country.

New York City is home to FABSCRAP, which is an organization that helps recycle and repurpose the fabric scraps and textile waste leftover by fashion designers, costume designers, interior designers and tailors.

And of course, you can always search for a local textile recycling service in your area.