Submandibular lymph node enlargement: This is a common and benign condition that can cause a lump under the chin. The lymph nodes in this area can become enlarged in response to minor infections or inflammation, and they often fluctuate in size.

Submandibular gland stone or obstruction: A stone or blockage in the submandibular gland can cause intermittent swelling under the chin, which may come and go without pain or tenderness.
Cystic hygroma or branchial cleft cyst: These congenital anomalies can present as a lump under the chin, which may fluctuate in size.
Thyroglossal duct cyst: A remnant of the thyroglossal duct can form a cyst under the chin, which may come and go without pain or tenderness.

Metastatic cancer: Although rare, a lump under the chin can be a sign of metastatic cancer, such as squamous cell carcinoma or lymphoma. It is essential to consider this possibility, especially in older adults or those with a history of cancer.
Tuberculosis or other granulomatous infections: These infections can cause lymph node enlargement or abscesses under the chin, which may be painless and intermittent.
Sarcoidosis: This autoimmune disease can cause lymph node enlargement and skin lesions, including under the chin.

Ranula: A type of mucous cyst that can form under the chin, usually associated with the sublingual gland.
Dermoid cyst: A congenital anomaly that can present as a lump under the chin, often containing hair, skin, or other tissue.
Lipoma or other soft tissue tumors: Benign tumors that can grow under the chin, although they are less common in this location.