Acne is a skin disorder resulting from the actions of hormones and other substances on skins oil glands and hair follicles. These things often lead to plugged pores and outbreak of lesions more commonly known as pimples and zits. Acne lesions basically occur on the face, back, chest, neck and shoulders. Thus acne is a term for plugged pores [blackheads and whiteheads], pimples and even deeper lumps [cysts and nodules] that appear in different parts of the body.

More: continued here