The skin is a dynamic barrier that protects the body from external sources of harm. One of the primary purposes of this barrier is to prevent infection. While the skin does provide protection from invading microorganisms, healthy skin contains a complex microbiota of normal, commensal microbial flora. An intricate balancing act exists between the skin and the wide array of microbes that constitute the normal flora. Environmental, physiological, biochemical, mechanical and immunological variables all contribute to maintain a healthy balance between the skin and its normal flora. When this balancing act is disrupted by internal or external forces, infection can occur. Infections can be caused by either normal commensal microbes or by external invading pathogens.