Some claim their pictures have been removed and their accounts blocked. This prevents breast cancer survivors from learning about possible treatments.
The campaigners said they should be able to post images of their experience without being wrongly sexualised.
Facebook rules do not allow nudity.
The platform does allow images of female breasts, including “those depicting acts of protest, women actively engaged in breastfeeding and photos of post-mastectomy scarring”.
But the protesters have urged Facebook to improve its algorithms to stop removing images posted by post-mastectomy patients who have had areola tattoos.
The protest was organised by areola tattooing group World Medical Artist.
Facebook said it was speaking to World Medical Artists about how to prevent medical tattoo images from being removed from the site.
The social media giant said it had restored all removed content that had been flagged to it by World Medical Artists.
— Vicky Martin Nipple Artist (@VickyMMethod) September 1, 2021
“Images showing post-mastectomy scarring and areola tattoos are absolutely allowed on Facebook and Instagram ” a company spokesperson said.
“We applaud the incredible work medical tattooists do for breast cancer survivors, and know our apps play an important role in helping these communities connect.
“By design, these tattoos often look extremely realistic, which means our technology – and even our content reviewers – don’t always spot the difference, so we do encourage people to make it clear when they’re posting an image that’s a tattoo.
“We understand how frustrating this can be. We’ve been working closely with World Medical Artists and are grateful for their input as we continue to explore new ways to avoid this content being mistakenly removed.”