Acne is the most common skin condition. It is caused by the bacteria Propionibacterium acnes (P.acnes in short). These bacteria live in our skin all the time. The bacteria creates a problem when a pore becomes blocked. The pore gets blocked when excess oil mixes with dead skin cells to form plug. Acne may be mild, moderate or severe. Severe acne can cause permanent scars. Acne can appear on the face, neck, back, chest, shoulders, upper arms and buttocks.