The most common cause of enlargement of the submental lymph nodes are infections (including viral infections (mononucleosis, Epstein-Barr virus infection, and cytomegaloviral infections), toxoplasmosis, and dental infections (e.g.
Submental lymph nodes often swell due to various infections, which can be caused by viral conditions like mononucleosis or Epstein-Barr virus, toxoplasmosis, and dental issues.