I have a painful whitish sore on my nipple. What is this?

Hi,

Welcome back to icliniq.com.

Thanks for your question. The areola and the areolar border is filled with modified sebaceous glands, called glands of Montgomery. They produce sebum, like those that form part of all your hair follicles. Thus they are prone to keratotic plug formation and then the build-up of debris and subsequent inflammation or infection just like other pimples on the rest of the body, especially the face, upper chest, and back. Treat it like another pimple by applying an anti-inflammatory or anti-microbial spot-treatment like Benzac AC (Benzoyl peroxide) and warm compresses with a warm cloth to help relieve duct obstruction and pain. Rarely it can lead to inflammation and infection of lactiferous ducts, causing mastitis. It would present as a swollen, warm and painful entire breast and requires oral antibiotics. But this is not what you currently have and the risk if it developing is low. The upper chest (in between breasts) is a common area for acne and cystic acne (large inflamed pimples) and what you describe fits well. It is best treated and followed up long term by your specialist dermatologist. Do not try to treat yourself as it will just lead to frustration.