What causes a lump under the armpit while breastfeeding?

Generally, a lump under the armpit during breastfeeding may be caused by accessory breast tissue, sebaceous cysts, enlarged lymph nodes, or other reasons. Specific details are as follows:
1. Accessory Breast Tissue
During lactation, if a patient already has accessory breast tissue, it may abnormally enlarge while breastfeeding. However, accessory breast tissue is usually soft in texture and does not typically cause significant pain.
2. Sebaceous Cyst
The armpit area contains numerous sebaceous glands. If proper cleaning is not maintained, secreted oils may become trapped, leading to local cyst formation and resulting in the aforementioned lump. Patients should visit a reputable hospital where doctors may recommend treatments such as isotretinoin and erythromycin gel or fusidic acid ointment.
3. Enlarged Lymph Nodes
If a patient develops mastitis during lactation, inflammatory stimulation can cause enlargement of the lymph nodes in the armpit. In such cases, patients may follow medical advice to take medications like cephalexin capsules or cefdinir dispersible tablets.
Besides the above, conditions such as mastitis, mammary gland hyperplasia, or even breast cancer could also be potential causes. Given the variety of possible underlying causes, individuals experiencing discomfort or other symptoms should promptly seek evaluation at a qualified medical facility to avoid delays in diagnosis and treatment.