Viral Parotitis (Mumps): This is often the first consideration due to its prevalence and the fact that it commonly causes parotid gland swelling. Mumps is a viral infection that primarily affects the parotid glands, leading to swelling and discomfort.

Bacterial Parotitis: This condition, often caused by Staphylococcus aureus, can lead to parotid gland swelling, especially in the context of decreased saliva production or ductal obstruction.
Sialadenitis: Inflammation of the salivary glands, which can be caused by bacterial or viral infections, and can lead to swelling of the parotid gland.
Benign Salivary Gland Tumors (e.g., Pleomorphic Adenoma): These are common tumors of the salivary glands and can cause swelling of the parotid gland.
Blockage of the Parotid Duct: Stones or other obstructions in the parotid duct can cause swelling by preventing normal saliva flow.

Parotid Gland Malignancy: Although less common than benign tumors, malignant tumors of the parotid gland can present with swelling and must be considered to ensure timely diagnosis and treatment.
Sjögren's Syndrome: An autoimmune disorder that can cause inflammation and swelling of the parotid glands, among other symptoms.
HIV-Associated Parotid Gland Disease: Certain conditions associated with HIV infection can cause parotid gland swelling, highlighting the importance of considering the patient's immune status.

Sarcoidosis: A systemic disease that can cause inflammation in various parts of the body, including the parotid glands, leading to swelling.
Tuberculosis: Although rare, tuberculosis can affect the parotid gland and cause swelling.
Parotid Gland Abscess: A collection of pus in the parotid gland, which is a rare but serious condition requiring prompt treatment.
Warthin's Tumor: A rare, benign tumor of the salivary glands that can cause parotid gland swelling.