Photographer Kai Lee publicly warned women about it, saying they need to think twice about taking part in the challenge.
"I keep seeing the Silhouette Challenge on my For You page, and even though they're all really cute and creative and y'all look bomb in them, just make sure you're being cognisant of what you're wearing before you actually do all the editing for the final product.
"Because anyone can easily take those images and revert them back to the original.
"So if you're wearing a bra and panties, or if you're nude, or whatever you did before you applied the editing to create that shadow look, just know that it's really easy to just put it back to the original."
Rolling Stone's culture writer EJ Dickson also warned of the trick, saying she has also seen disturbing tutorials on how to revert the image back to the original.
Obviously not linking, but there are videos all over YouTube offering tutorials for how to "remove" the red filter for TikTok's Silhouette Challenge, in which women dance nude or partially nude in silhouette.
"This is a huge consent violation and YouTube should remove them ASAP.
"Some of these videos are monetised.
"Literally my mentions have been flooded with dudes saying these women deserve it and I've been blocking people left and right so I guess do your worst gentlemen."
Unfit Christian Blogger Danyelle Thomas also warned her followers to be careful.
"Men are currently removing the vin rouge red filter from the silhouette challenge. This is readily happening across social media with little community violation response by Facebook, Twitter, Instagram, Snapchat, or TikTok.
"When reminded that this is gross, creepy, and nonconsenting, men respond that women are always finding ways to make themselves victims and they shouldn't have been naked on the internet.
"Yes, the same men going through extraordinary lengths to be creepy are finger-wagging women about what they shouldn't put on the internet.
"Because of all of the things men lack – including ethics and boundaries – they're never short on audacity. This is when rape culture, misogyny and patriarchal malarkey combine."