Actors Mark Ruffalo and Samuel L. Jackson are among celebrities supporting the 'One For The Boys', campaign which raises awareness about male breast cancer.
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."
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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.