Enlarged lymph nodes under the armpit can be caused by various factors, including infections, injuries, autoimmune disorders, and cancer. Some of the common causes of swollen lymph nodes in the armpit are:

• Infections: Bacterial or viral infections can cause the lymph nodes to swell. Some examples of infections that could affect the nodes in the armpit include cellulitis, flu, mono, and common viruses.

• Autoimmune disorders: Flare-ups of autoimmune disorders, like lupus and rheumatoid arthritis, can cause temporary enlargement of the lymph nodes in an armpit.

• Cancer: Rarely, swollen lymph nodes are caused by cancer. Lymphoma (cancer of the lymphatic system) is one of the cancers that can cause swollen lymph nodes in the armpit.

It is important to note that swollen lymph nodes in the armpit are not always a sign of cancer. A doctor can determine the cause of swollen lymph nodes in the armpit and recommend the best treatment. They may ask about the person’s symptoms, review their medical history, and perform a physical examination. In some cases, a doctor may also carry out diagnostic tests, such as blood tests, a biopsy, or medical imaging.