They took to Twitter on Tuesday to share images of themselves baring their nipples, reports aceshowbiz.com.
The “Infinitely Polar Bear” actor posted a photograph of him uncovering his chest. While showing a smile to the camera, Ruffalo was pointing at his nipple.
“Men get breast cancer too. I’m supporting @One4TheBoys #InTheNipOfTime campaign,” read the caption.
Jackson, meanwhile, opted to post on the micro-blogging site an image of his nipple.
The “Kingsman: The Secret Service” actor captioned the image: “Checkin’ Myself before I Wreck Myself! Taken #InTheNipOfTime All in aid of @One4theBoys Get Ur Nips Out! Your Turn!”
In response to his tweet, the charity posted: “Huge thanks to @SamuelLJackson for supporting #InTheNipOfTime with his selfie. Not an easy thing to do, but neither is talking about cancer.”
Scottish rugby union footballer Jim Hamilton also posted a black-and-white picture of him shirtless in a locker room.
Alongside the image, he wrote: “Raising awareness for breast cancer in men @One4theBoys #InTheNipOfTime #tweetyournipple #nippleselfie.” He also posted some pictures of fellow athletes.
Other celebrities who joined the campaign included Lionel Richie and Matthew Perry.
Instead of posting their shirtless photographs, they opted to post a video created by the charity to encourage men to find information regarding the signs associated with cancer.