Though perceived to be a growing problem by lactation professionals, fungal infection of the breast (mammary candidosis) is largely unstudied. Candida albicans, a commensal organism encountered frequently in the vagina and gastrointestinal tract of humans, has been reported to be responsible for both superficial (cutaneous) and localized (ductal) infection of the mammary gland in lactating women, though the latter association is not universally accepted. Severe pain is considered to be characteristic of yeast infection of the breast and may be a cause of premature weaning among lactating mothers. Given that pain is often the complaint that prompts mothers to consult lactation professionals, it is important that healthcare providers working with lactating women be knowledgeable about this disease. In this article, current research regarding yeast infection of the breast is summarized, including morphology and pathology, diagnosis, risk factors, and common treatment options.