Fashion brands are among the most prolific advertisers on so-called alt-right site Breitbart, thanks to retargeting, which this sector appears to adore using.

A jaunt on Breitbart shows ads for Madewell, Saks Fifth Avenue, Yoox, Net-a-Porter, Swarovski and Tarte Cosmetics, among many others.

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It’s a strange ad buy: Breitbart isn’t necessarily the audience these brands want to reach. Breitbart had 19 million unique visitors in October. Its audience skews heaviest toward males between 25 and 65 (especially between 45 years and 64 years), per comScore.

But in some ways, it makes sense. Adam Broitman, managing partner at digital media buying agency MEC, which buys ads for brands, said that while it may seem weird to have fashion brands on a site like Breitbart, margins are so low in retail that the brands essentially take what they can get. “When you’re talking about a retailer, they’re going to gravitate toward the highest ROI,” he said.

Many brands don’t know they’re even advertising on Breitbart. Because of the way digital advertising works, brands often buy “audiences,” which means groups of people, programmatically. Often, ads are served up based on audiences, not the publisher. Most of the ads on Breitbart are served through retargeting, which delivers ads based on your browsing history.

The other way fashion brands are getting on the site are thanks to Google. With Google behind the ads, the ads line up with your interests. If you’re tagged for “fashion” or “beauty,” you get served those ads, regardless of what site you’re viewing.

Many brands seem completely unaware of how programmatic advertising is serving up their ads and where. A rep for Modcloth, one of the brands that previously had ads on the site, said, “Like so many other brands, we were not aware of the placement. Once we were made aware is when we made the decision.”

Broitman said that, for brands, retargeting ads means that someone was on their site at some point — and therefore a potential customer. The rest, they don’t care about.

With Donald Trump appointing Steve Bannon, the former chairman of Breitbart, into a top post in the administration, a conversation has erupted over sites like Breitbart, and inevitably shone light into an issue for brands in digital media: Programmatic advertising is a black box that puts your ads in places you may not know they’re running. While blacklisting or whitelisting sites is possible, it’s a hard decision to make since brands often may not know what to actually filter for. And fashion brand marketers, said one buyer, are often even less in the know: The industry tends to be less knowledgeable about programmatic marketing and digital media than others, said this buyer. Broitman agreed: “It’s more of a black box for them, always has been.”

Brands have been on the defensive since last week, when a social media storm asked a bunch of advertisers to blacklist Breitbart and pull their ads from the conservative site because of its anti-Semitic, sexist and racist stories.

A large part of the social media maelstrom was driven by a Twitter account called Sleeping Giants, which is mobilizing people to tweet at brands who have advertising featured on Breitbart.

About 47 brands to date have confirmed to the account that they’re supposedly blacklisting the site. Breitbart, on its end, is asking its readers to boycott one of those brands, Kellogg’s.