Just noticed small bumps under skin on top of the part of ribs that stick out (aka rib flare) what are possible causes? is it most likely be benign?

Doctor can examine: Bumps under the skin are hard to figure out without an exam. Sometimes, they appear and disappear for unknown reasons. Bumps may be ok if there is no pain, oozing, bleeding, itching, etc... A doctor can look at the bumps, examine them by using her hands, to help get a diagnosis. Guesswork won't be useful in this case. An in-person exam will help.