Causes Species The causative organism is usually Candida albicans, or less commonly other Candida species such as (in decreasing order of frequency) Candida tropicalis, Candida glabrata, Candida parapsilosis, Candida krusei, or other species (Candida stellatoidea, Candida pseudotropicalis, Candida famata, Candida rugosa, Candida geotrichium, Candida dubliniensis, and Candida guilliermondii). C. albicans accounts for about 50% of oral candidiasis cases, and together C. albicans, C. tropicalis and C. glabrata account for over 80% of cases. Candidiasis caused by non-C. albicans Candida (NCAC) species is associated more with immunodeficiency. For example, in HIV/AIDS, C. dubliniensis and C. geotrichium can become pathogenic. About 35-50% of humans possess C. albicans as part of their normal oral microbiota. With more sensitive detection techniques, this figure is reported to rise to 90%. This candidal carrier state is not considered a disease, since there are no lesions or symptoms of any kind. Oral carriage of Candida is pre-requisite for the development of oral candidiasis. For Candida species to colonize and survive as a normal component of the oral microbiota, the organisms must be capable of adhering to the epithelial surface of the mucous membrane lining the mouth. This adhesion involves adhesins (e.g., hyphal wall protein 1), and extracellular polymeric materials (e.g., mannoprotein). Therefore, strains of Candida with more adhesion capability have more pathogenic potential than other strains. The prevalence of Candida carriage varies with geographic location, and many other factors. Higher carriage is reported during the summer months, in females, in hospitalized individuals, in persons with blood group O and in non-secretors of blood group antigens in saliva. Increased rates of Candida carriage are also found in people who eat a diet high in carbohydrates, people who wear dentures, people with xerostomia (dry mouth), in people taking broad spectrum antibiotics, smokers, and in immunocompromised individuals (e.g., due to HIV/AIDS, diabetes, cancer, Down syndrome or malnutrition). Age also influences oral carriage, with the lowest levels occurring in newborns, increasing dramatically in infants, and then decreasing again in adults. Investigations have quantified oral carriage of Candida albicans at 300-500 colony forming units in healthy persons. More Candida is detected in the early morning and the late afternoon. The greatest quantity of Candida species are harbored on the posterior dorsal tongue, followed by the palatal and the buccal mucosae. Mucosa covered by an oral appliance such as a denture harbors significantly more candida species than uncovered mucosa. When Candida species cause