A rash under the breasts usually causes a great deal of concern to patients, but the problem can have a wide variety of causes - sometimes the lesions in the breast area are the result of atopic dermatitis or contact eczema, and they can also be caused by parasitic or viral infections. How can you tell what the cause of a rash under the breasts is - when should a patient absolutely go to see a doctor immediately, and when can a visit to a specialist be postponed a little?