Acne typically appears on your face, forehead, chest, upper back and shoulders because these areas of skin have the most oil (sebaceous) glands. Hair follicles are connected to oil glands. The follicle wall may bulge and produce a whitehead. Or the plug may be open to the surface and darken, causing a blackhead.Four main factors cause acne: 1. Excess oil (sebum) production 2. Hair follicles clogged by oil and dead skin cells 3. Bacteria 4. Inflammation Acne typically appears on your face, forehead, chest, upper back and shoulders because these areas of skin have the most oil (sebaceous) glands.