Hygiene is important for keeping you well and for preventing the spread of disease. In the recent Ebola outbreak, those with no access to soap and water were the most likely to become victims, whole families being wiped out. When aid came, the vital approach was to get washing facilities to homes and whole communities. Hygiene is evolutionarily important, as can be evidenced in the animal world.
Species have evolved hygienic behaviors: even ants groom themselves to remove fungal pathogens. Species that survive are those with hygienic approaches to risk. Even sheep avoid fecal matter, and animals such as badgers and lemurs use latrines. It is basic to avoid disease and contamination, and this is the function of hygiene.