Acne is a skin condition that occurs when your hair follicles become plugged with oil and dead skin cells. Acne most commonly appears on your face, neck, chest, back and shoulders. Acne can be distressing and annoyingly persistent. Acne lesions heal slowly, and when one begins to resolve, others seem to crop up.
Depending on its severity, acne can cause emotional distress and lead to scarring of the skin. The good news is that effective treatments are available — and the earlier treatment is started, the lower your risk of lasting physical and emotional damage.
Three factors contribute to the formation of acne:
• Overproduction of oil (sebum)
• Irregular shedding of dead skin cells resulting in irritation of the hair follicles of your skin
• Buildup of bacteria
Acne occurs when the hair follicles become plugged with oil and dead skin cells. Hair follicles are connected to sebaceous glands. These glands secrete an oily substance known as sebum to lubricate your hair and skin. Sebum normally travels up along the hair shafts and then out through the openings of the hair follicles onto the surface of your skin. When your body produces an excess amount of sebum and dead skin cells, the two can build up in the hair follicles and form together as a soft plug, creating an environment where bacteria can thrive.
This plug may cause the follicle wall to bulge and produce a whitehead. Or, the plug may be open to the surface and may darken, causing a blackhead. Pimples are raised red spots with a white center that develop when blocked hair follicles become inflamed or infected. Blockages and inflammation that develop deep inside hair follicles produce lumps beneath the surface of your skin called cysts. Other pores in your skin, which are the openings of the sweat glands onto your skin, aren't normally involved in acne.
Source: Mayo Clinic