Yeast Infection (Candidiasis) : Candidal infections commonly occur in warm moist body areas, such as underarms. Usually your skin effectively blocks yeast, but any breakdown or cuts in the skin may allow this organism to penetrate. In adults, oral yeast infections become more common with increased age. Adults also can have yeast infections around dentures, under the breast and lower abdomen, nailbeds, and beneath other skin folds. Most of these candidal infections are superficial and clear up easily with treatment. Rarely, the yeast infection may spread throughout the body. In systemic candidal disease, up to 75% of people may die. Even common mouth and vaginal yeast infections can cause critical illness and can be more resistant to normal treatment. Yeast infections that return may be a sign of more serious diseases such as diabetes, leukemia, or AIDS.