Plasmacytic mastitis, also called ductal dilatation, is called acantholytic canker sores in Chinese medicine. Plasmacytosis is different from the usual purulent mastitis during lactation. Many people do not recognize this disease and mistake it for a general bacterial infection, or misdiagnose it as breast tuberculosis, or, most frighteningly, misdiagnose it as breast cancer mistakenly cutting the breast. Plasmacytoid mastitis is a relatively complex inflammatory disease of the breast, so named because of the large number of plasma cells infiltrating the tissue surrounding the inflammation. The disease is caused by irregular hyperplasia of the epithelium of the breast ducts, secretion dysfunction, and accumulation of lipid-laden secretions in the large milk ducts under the nipples and areola, causing dilation of the milk ducts, and later decomposition of the accumulation, which produces chemicals that constantly stimulate the surrounding tissues and cause inflammation. Sometimes the inflammation can become acute and become an abscess, so the pus is often laden with bean curd-like or powder-like material, so it is also called “acne mastitis”. Nipple deformities also inevitably cause distortion and deformation of the ducts. The ducts are then easily blocked, and the duct contents are lipidic substances that leach the duct walls causing overflow, causing chemical inflammation, and a large number of lymphocytes and plasma cells react to form small inflammatory masses. Therefore, one should understand plasma milk, not delay the diagnosis, and strive for a one-time cure. Plasmacytoid mastitis has a sudden onset and develops rapidly. The patient feels localized pain and discomfort in the breast, and a lump may be palpable. The lump is located under the areola or extends into one quadrant. The masses are hard. The surface is nodular, with poorly defined borders and no adhesions to the chest wall. The skin of some breasts is edematous and orange peel-like, and there are usually no systemic symptoms such as fever. The nipples are often edematous and orange peel-like. The nipples often secrete powder-like material with a foul odor. A small number of patients have nipple discharge, which is bloody or watery, and may be accompanied by enlargement of the axillary lymph nodes on the affected side. In the late stage, the lump becomes softened and forms an abscess. When the abscess breaks down, pus mixed with powder-like pus flows out and causes fistulas in the areola, resulting in recurrent wounds and scarring, making the nipple sunken into a concave.