Antibiotic and antimicrobial resistance is an important topic in modern medicine. Bacteria develop chemical resistance by the process of evolution; in most populations of bacteria, a few individuals will exhibit better tolerance toward antibacterial agents than average. If the population is treated lightly with an antibacterial, the susceptible majority will be killed off, leaving the resistant individuals to repopulate the area; this process creates a resistant population.
Traditional soaps do not kill bacterial, they just help to remove them from surfaces, so bacteria are unable to develop a resistance to regular soaps. Sanitizers and antibacterial soaps, however, do depend on antibacterial chemicals and can lead to resistance. Here is a link to an article describing the development of resistance in response to a number of antimicrobial agents including triclosan, one of the leading sanitizer chemicals.