Viral upper respiratory infection: This is the most common cause of swollen lymph nodes in the general population, especially when the swelling is localized and accompanied by other symptoms like a sore throat or runny nose. The location in front of the ear suggests involvement of the parotid or preauricular lymph nodes, which can be reactive to infections in the ear, throat, or face.

Dental infection: Infections of the teeth or gums can cause swelling of the lymph nodes in the face and neck, including those in front of the ear. This is due to the drainage of the facial and dental areas into these lymph nodes.
Ear infection: Both outer ear (otitis externa) and middle ear (otitis media) infections can lead to swollen lymph nodes in front of the ear due to the direct lymphatic drainage from the ear to these nodes.
Skin infection: Localized skin infections (cellulitis, abscesses) on the face or scalp can cause reactive lymphadenopathy in the nearby lymph nodes, including those located in front of the ear.

Lymphoma: Although less common, lymphoma (both Hodgkin and non-Hodgkin types) can present with lymphadenopathy that may be localized or generalized. It's crucial to consider this diagnosis, especially if the lymph node swelling is persistent, painless, and accompanied by systemic symptoms like weight loss or fever.
Tuberculosis: TB can cause lymphadenitis, particularly in the cervical lymph nodes, but it can also affect nodes in other locations, including in front of the ear. This diagnosis is especially important to consider in individuals with risk factors for TB exposure.
Cat-scratch disease: Caused by Bartonella henselae, this infection typically presents with a scratch or bite wound followed by regional lymphadenopathy, which can occur in front of the ear if the initial injury was on the face.

Sarcoidosis: A systemic granulomatous disease that can cause lymphadenopathy among other symptoms. It's less common but should be considered in the differential diagnosis of persistent lymph node swelling without an obvious infectious cause.
Kawasaki disease: An acute febrile illness of childhood that can present with lymphadenopathy, among other criteria like fever, rash, and conjunctivitis. It's rare but important to recognize due to its potential for cardiac complications.
Parotid gland tumors: Both benign (like pleomorphic adenoma) and malignant tumors of the parotid gland can present with a mass in front of the ear, which might be mistaken for lymphadenopathy.