Zac Efron's facial changes primarily stem from a serious jaw injury he suffered in 2013. While running in socks at home, he slipped and hit his chin against the granite corner of a fountain, resulting in a severe fracture where his chin bone was nearly detached. This injury required surgery to reconstruct his jaw and extensive physical therapy for recovery

. The injury caused his masseter muscles-the muscles used for chewing-to overcompensate, growing larger and altering the shape of his jawline and face. This muscle enlargement, combined with periods where he paused physical therapy, led to a more sculpted and noticeably different jawline compared to his earlier, more oval-shaped face

. Despite widespread rumors, Zac Efron has denied undergoing cosmetic surgery like facelifts or fillers. However, speculation persists about possible minor cosmetic procedures such as Botox to maintain skin smoothness and a rumored subtle nose refinement, though these remain unconfirmed

. His transformation was also influenced by his physical preparation for roles like "The Iron Claw," where he gained significant muscle mass, further changing his overall appearance

. In summary, Zac Efron's altered facial appearance is mainly due to the aftermath of his 2013 jaw injury and the body's natural response during recovery, rather than elective plastic surgery