A new research paper from Princeton University has found that 90 percent of affiliate posts on YouTube and Pinterest aren’t disclosed to users.

Affiliate links are customized URLs that content publishers can include in their posts. They’re essentially ads, and publishers receive money from companies when users click on them. In the US, the Federal Trade Commission (FTC) requires that content makers identify when they’re being paid to post something, but despite that, influencers continue to skirt around disclosures. The FTC has previously sent out letters to influencers reminding them of the requirement to communicate paid relationships with brands to their followers.

The paper from Princeton analyzed over 500,000 YouTube videos and 2.1 million unique pins on Pinterest. Of those, 0.67 percent, or 3,472 videos on YouTube, and 0.85 percent, or 18,237 pins, contained affiliate links.

Sponsored content posted by influencers aren’t always identified as such, making it harder for consumers to tell the difference between original content and advertisements. The paper, written by Arunesh Mathur, Arvind Narayanan, and Marshini Chetty, collected data between August and September 2017 and outlines three main findings:

Prevalence of disclosures is low, with only about 10 percent of affiliate content on YouTube and Pinterest tagged as such

On both Youtube and Pinterest, user engagement was higher on posts that contained affiliate links

Marketing affiliate disclosures were formatted in three different ways: affiliate link disclosures like the phrase “#affiliatelink”; explanation disclosures like “This video contains affiliate links, which means that if you click on one of the product links, I’ll receive a small commission”; and support channel disclosures that state, “AMAZON LINK: (Bookmark this link to support the show for free!!!”)

The FTC says just stating that a link is sponsored isn’t enough, and publishers should use a short phrase that clearly says they’re being paid when a link is clicked. Having disclosures is important, the Princeton paper notes, because posts with affiliate links usually get more engagement from users. This means they’re more likely to be picked up by algorithms and shown to users through search or in their feeds. The paper states:

Concerningly, our results show that the overall prevalence of affiliate disclosures is low, and that the disclosures are largely of the variety the FTC specifically advocates against: the Affiliate Link disclosures. In fact, Explanation disclosures—which the FTC recommends—only appear in 1.82% and 2.43% of affiliate content on YouTube and Pinterest respectively.

Affiliate links were mostly found on YouTube in videos about science and technology, style, travel and events, and film and animation. On Pinterest, posts with affiliate links were mostly included in pins related to women’s fashion, products, hair and beauty, and sports.

Continuing my theme of exciting research with depressing conclusions: we analyzed 500k YouTube videos & 2 million Pinterest pins, finding that 90% of affiliate marketing is not disclosed to users, in violation of FTC guidelines and other regulations. https://t.co/4m7X1xHANM — Arvind Narayanan (@random_walker) March 26, 2018

The researchers note that social media platforms play a crucial role in how affiliate links are presented, and pointed to YouTube’s paid endorsements tool and Instagram’s recent disclosure feature that displays a “paid partnership” branding on sponsored posts.

“Such disclosure tools are a step in the right direction, however it is unlikely that such blanket disclosures will cover all marketing strategies,” the researchers wrote. “Future work could investigate what kind of affordances should be designed into social media platforms to enable affiliates to disclose clearly.” The researchers said companies paying content publishers to post sponsored content should also be held accountable for better disclosure practices.

In the future, the researchers said they hoped to build a tool like a browser extension that detects affiliate content that might be buried in posts, and highlight them to users.