Many people go through rotations of dresses every December for countless holiday and New Year’s parties, but for those participating in Dressember, getting dolled up comes with a dose of do-gooding.

“Dressember is an annual campaign where people wear dresses every day during the month of December as a way to raise awareness and money for anti-trafficking organizations,” the organization’s cofounder and chief executive officer Blythe Hill explains. “We focus specifically on sex trafficking, but there are all forms of trafficking as well that go into it. “

Hill got the idea for the dress-a-day style challenge in college, and later connected it with her passion for eradicating sex trafficking.

“There are more people alive today in slavery than ever before in history — the numbers are upward of 36 million people. It’s a $150 billion industry and the vast majority of people trapped in trafficking are women and girls. It’s one of the fastest-growing criminal industries,” she says. “When I started hearing about it I was in college and I just felt this immediate urgency to do something about it. At the time, I was an English major and didn’t know [what to do]. I was like, ‘OK, should I reroute my career toward criminal justice?’ And I just didn’t feel at peace about doing that, so struggled for years with feeling this tension and powerlessness.”

Meanwhile, she was in need of a “creative outlet” so decided to give herself a style challenge to wear a dress every day for a month and document her experiences on a blog. “The month happened to be December and I came up with the name ‘dressember.’ The next year my girlfriends brought it up and wanted to do it, and the year after that their girlfriends brought it up and wanted to do it,” she says. “So at that point when there were people who I didn’t know personally, I knew it was a good idea.”

The challenge is not limited to women — Hill notes that “anyone can wear a dress” — so those who aren’t comfortable in a dress have begun wearing bow ties or ties as a “Dressy-ember.”

Hill likens the process to Race for a Cure or like-minded fund-raising efforts; participants can create their own page for fund-raising and send it out to family and friends, notifying them of the Dressember challenge.

“In 2013, I reached out to the anti-trafficking organization International Justice Mission, the largest anti-trafficking organization in the world,” Hill says, adding that “1,200 people signed up that first year, and my initial goal had been $25,000 which to me felt really scary, and we hit that on the third day of the month.” This is the fourth campaign year; the first three years yielded $3 million, with 6,000 participants last year. With the end of the month looming, they’ve surpassed the $1 million mark.

Dressember has begun offering dresses for sale on its web site, made by survivors of sex trafficking in Nepal, who are “given a fair wage,” as several women who were interested in participating were cautious about buying clothing made in unsafe working conditions for women around the world.

“Unfortunately labor trafficking is so prevalent in the fashion industry, especially with fast fashion,” Hill explains.

“I hear women say I hate wearing dresses, but I hate this issue more.”