Sialadenitis: This is an inflammation of the salivary glands, which can be caused by bacterial or viral infections. It is the most common cause of parotid gland edema due to its frequency and the parotid gland's susceptibility to infection.

Parotid gland tumor: Both benign (like pleomorphic adenoma) and malignant tumors can cause edema by obstructing the flow of saliva or through local invasion.
Sjögren's syndrome: An autoimmune disorder that can cause inflammation and swelling in the parotid glands among other symptoms.
Allergic reactions: Allergic reactions to foods, medications, or other substances can cause swelling in the parotid gland.

Parotid gland abscess: Although less common, an abscess in the parotid gland can be life-threatening if not promptly treated, especially if it leads to sepsis or spreads to other areas of the head and neck.
Necrotizing sialometaplasia: A rare, potentially life-threatening condition that can mimic a malignant process and requires prompt diagnosis and treatment.
Sarcoidosis: A systemic disease that can affect multiple organs, including the parotid glands, and if missed, can lead to significant morbidity.

Kimura disease: A rare, chronic inflammatory disorder that can cause swelling in the parotid gland and is often associated with lymphadenopathy and eosinophilia.
IgG4-related disease: A systemic fibroinflammatory condition that can affect the parotid glands among other organs, leading to swelling and dysfunction.
Wegener's granulomatosis (Granulomatosis with Polyangiitis): A rare autoimmune disorder that can affect the parotid glands and other parts of the body, leading to significant complications if not treated.