According to a study from Northwestern Medicine and published in the Aesthetic Surgery Journal, Instagram is being used to advertise plastic surgery services, but not just by board-certified plastic surgeons.

The study looked at nearly 1.8 million posts that contained 21 plastic surgery-related hashtags, such as #plasticsurgery, #facelift, #breastimplant, #liposuction, and #nosejob. Of these, they looked deeper into the top nine posts for each of the hashtags.

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The largest number of posts came from foreign surgeons, but the second largest number came from doctors that are not certified to perform plastic surgery. These included dermatologists, dentists, gynecologists, or spa aestheticians. Legally, any licensed doctor can perform cosmetic surgery, but without certification their level of training can vary. According to the study, only 17.8% of the posts came from board-certified plastic surgeons.

The study’s senior author, Dr. Clark Schierle, told CNN that “some of these are doctors practicing outside of their scope of practice. Some of these are non-physicians just doing crazy stuff, like injecting silicone building material from Home Depot into people’s bodies without a medical license.”

With more and more people—particularly millennials—turning to Instagram as a one-stop shop for everything from buying clothes or medications and supplements to finding a plastic surgeon, the inability to distinguish between certified and non-certified surgeons is potentially risky. However, the study only looked at posts from a single day, so more data will need to be collected over time to reveal broader trends.