Active Acne
Normally, dead cells collect in the skin's pores, then slowly rise to the surface of the openings and eventually fall away from the skin. A natural body oil called sebum helps to prevent skin cells from drying out. The glands that produce this oil are attached to the pores. When excess sebum builds up, it can cause dead cells to stick together, forming a mixture that becomes trapped in the pores.
Acne occurs when a pore becomes clogged with dead skin cells, natural body oils, and a type of bacteria. These bacteria live on the skin and are called Propionibacterium acnes. If they enter and infect clogged pores, this causes acne blemishes to form.