The vast majority of teenagers will get acne at some point, as shifts in hormone levels stimulate oil glands to produce high levels of sebum (skin oil) and it combines with dead skin cells to clog pores. Clogged pores can become inflamed, leading to pimples on the face, neck, back, chest and shoulders. Acne usually makes an appearance during adolescence years, specifically the pre-teen and teenage time frame, though as