Dec 07, · A red spot on breast can be as a consequence of having fungal or yeast infection. The infection of candida on the skin can result in red patches under the breast surface. Yeast infection can also affect the entire skin surface of the bread with red tiny itchy rashes. Yeast infection is a prevalent condition in the hot and moist environment. Aug 17, · Most breast rashes have the same causes as rashes occurring elsewhere on the body. Some rashes occur only on the breast. Causes of rash that occur only on the breast may include: Breast abscess; Inflammatory breast cancer; Mammary duct ectasia; Mastitis (an infection in breast tissue that most commonly affects women who are breast-feeding.