Eczema or contact dermatitis is a very common cause of an itchy, red, scaly nipple or areola. It can follow a new soap, detergent, cream or bra fabric, and it usually affects both sides. A fungal infection in the fold under the breast gives a red, itchy rash there, especially in humid weather.
An infection of the breast, called mastitis, causes a red, hot, tender area, most often in breastfeeding women, and may come with fever. Fat necrosis, a firm area that forms after an injury or surgery, can pull the skin into a dimple. A widened milk duct can draw the nipple inward in some women later in life.
Less often, a skin or nipple change is caused by cancer. Paget disease of the nipple is a rare form that looks like eczema on one nipple, with scaling, crusting or a red patch that does not heal. Inflammatory breast cancer is also rare. It causes a red, swollen, warm breast with orange-peel skin that develops over weeks, often without a distinct lump. Because these look like common conditions, a change that is new, one-sided and lasting should be examined.