There are more than 100,000 known fungi, but only few invade human tissues. These fungi are common saprophytes of soil and decaying vegetation, and person to person transmission is rare, but Candidais an exception. In human tissues the fungi can be seen as yeasts or molds. Oral infections are also common in babies and denture wearers, in individuals who use inhaled steroids for asthma, in leukemia and transplant patients, and in people who have had radiotherapy for head and neck cancers. These superficial infections are caused most often by several species of Candida, which are the second most numerous agents of fungal infection worldwide.