What causes a hard lump under the armpit after giving birth?

Generally, the presence of lumps under the armpit after childbirth may be caused by factors such as reactive lymph node hyperplasia, breast tissue proliferation, folliculitis, sebaceous cysts, or mastitis. If any abnormalities occur, it is recommended to seek medical attention promptly. Detailed analysis is as follows:

1. Reactive Lymph Node Hyperplasia

During childbirth, the body undergoes a certain degree of stress and inflammatory response, which may cause lymph nodes—part of the immune system—to exhibit mild reactive hyperplasia. In most cases, reactive lymph node hyperplasia does not require treatment and resolves spontaneously.

2. Breast Tissue Proliferation

During pregnancy, elevated hormone levels such as estrogen and progesterone stimulate breast tissue growth. Sometimes this tissue extends into the armpit area, forming what is known as "accessory breasts." This condition is usually benign and related to changes in breast tissue during lactation. Typically, no specific treatment is required.

3. Folliculitis

Folliculitis may be caused by bacterial or fungal infections. After childbirth, decreased immunity and inadequate skin hygiene may trigger folliculitis. It can lead to redness, swelling, pain around hair follicles, and the formation of firm lumps. Local itching may accompany the condition, and severe inflammation may result in pus formation. It is recommended to use medications such as mupirocin ointment, cefuroxime axetil tablets, or fusidic acid sodium ointment under a doctor’s guidance to control the condition.

4. Sebaceous Cyst

A sebaceous cyst forms due to blockage of the sebaceous gland duct, leading to retention of sebum and gradual expansion of the cystic epithelium. Postpartum factors such as reduced immunity and poor skin hygiene may contribute to the development of sebaceous cysts. Usually, there are no significant symptoms, but larger cysts may press on surrounding tissues and cause pain. Mild sebaceous cysts can be monitored conservatively with attention to skin cleanliness. If the cyst is large or affects appearance, surgical removal may be considered.

5. Mastitis

Lactating women after childbirth are prone to mastitis due to milk stasis or nipple damage. Inflammation can affect breast tissue and nearby lymph nodes, resulting in hard lumps. Symptoms may include breast pain, redness, swelling, and fever. Severe cases may present systemic symptoms such as chills and high fever. Treatment may include antibiotics such as amoxicillin capsules, oxacillin sodium capsules, or cefradine capsules, as prescribed by a physician.

Postpartum lactating women can engage in moderate exercise, such as yoga or Pilates, to support physical recovery. Targeted exercises may help manage conditions like accessory breasts if they occur.