Thrush infection of the tongue. Animated coloured scanning electron micrograph (SEM) of a fractured tongue infected with Candida sp. fungus (orange), known as yeast infection, thrush, or candidiasis. Candida doesn't become a problem until there's a change in the chemistry of the oral cavity that favours candida over the other micro-organisms that are present. These changes can occur as a side-effect of taking antibiotics or drug treatment, such as chemotherapy. These changes can also be caused by certain conditions such as diabetes, drug abuse, malnutrition and as a consequence of immune deficiencies relating to old age or infection such as AIDS.