Acne is a single disease with multiple causes and a variety of manifestations. When a pilo-sebaceous unit becomes inflamed it appears as a raised red painful bump on the skin called a papule or pimple. When a pore gets blocked by oils and dead skin cells it appears as a white dilated pore called a whitehead. When these oils and dead skin cells reach the surface of the pore they darken and are now called blackheads. When bacteria multiple within a clogged pore the result can be inflammation with pus filling the pore and is now called a pustule. Sometimes the chronic inflammation that results from acne can result in multiple hard bumps below the skin surface called nodules. This nodular type of acne can last for months and is frequently associated with scarring. By reducing the severity and frequency of breakouts this common side effect can be avoided.