BACKGROUND: Non-lactational Mastitis of Accessory Breast (NLM-AB) is a rare condition with limited research, leading to diagnostic challenges. Its clinical and demographic characteristics are poorly defined, and it is often confused with non-lactational mastitis (NLM), hindering effective diagnosis and treatment. OBJECTIVE: This study aims to clarify the features of NLM-AB, distinguish it from NLM, and address key knowledge gaps to improve clinical diagnosis and patient management. METHODS: We retrospectively analyzed data from 31 NLM-AB patients treated at Beijing Hospital of Traditional Chinese Medicine from January 2014 to September 2024. A 1:1 matched case-control study was conducted, comparing NLM-AB (case group) with 31 NLM patients (control group). RESULTS: NLM-AB patients had a mean age of 36.68 ± 7.17 years and BMI of 23.10 ± 3.52. Most were married (83.87%) and had given birth (58.06%). All had axillary masses, with 85.19% showing skin changes. Statistically significant differences were found in marital status, reproductive history, breastfeeding duration, tumor size, and nipple retraction (P 0.05). CONCLUSION: This study addresses a key clinical gap by identifying distinguishing features of NLM-AB, such as consistent axillary masses without nipple retraction and associations with reproductive history. These findings can directly support clinicians in early recognition and differential diagnosis of NLM-AB, avoiding unnecessary interventions targeting primary breast tissue. Incorporating these patient characteristics into diagnostic pathways may reduce misdiagnosis rates and guide more tailored treatment strategies, ultimately improving patient outcomes.