Some rashes occur only on the breast.Causes of rash that occur only on the breast may include:Breast abscessInflammatory breast cancer Mammary duct ectasia Mastitis Nipple dermatitisNipple piercings or other body art, such as tattooingPaget's disease of the breast Radiation dermatitisGeneral causes of rash that can affect any part of the body, including the breast, include:Atopic dermatitis (eczem