It is estimated that at any given time, approximately 30% of the healthy human population has staph present on their skin or in their mucous membranes such as the nose or mouth. Most people have been exposed to staph at one time or another in their life. Usually S. aureus lives on the skin without causing any harm or disease. However, damaged skin, injuries, indwelling devices such as implants and catheters, etc. can allow the bacteria to overcome the natural immune response of the body and lead to a potentially severe infection.