Tonsil cancer, which involves tonsils located on the sides of the throat, causes an enlargement of one of the tonsils, explains Cedars-Sinai. Additional symptoms of tonsil cancer include severe ear pain, persistent sore throat and painful swallowing. Other causes of an enlarged tonsil include tonsillitis, tonsil stones and peritonsillar abscess.
Inflammation of lymphatic tissue on the side of the throat causes tonsillitis. Its symptoms include difficulty swallowing, sore throat and pain on one side of the throat caused by a swollen tonsil. If left untreated, the condition may cause heart and lung problems, Providence Health and Services reports.
Tonsil stones contribute to an enlarged tonsil when dead cells and debris accumulate around a tonsil, causing it to harden and enlarge over time, according to WebMD.
Peritonsillar abscess is a complication that results from tonsillitis. An infection may lead to a pus-filled swelling in the space lying between the tonsils and the throat that is known as the peritonsillar space. The swelling pushes against the closest tonsil, causing it to enlarge and, in severe cases, impair breathing, according to Drugs.com. Without urgent treatment, the infection may spread to the mouth or lungs. The abscesses mostly affect young adults and older children.