Causes for swelling of the parotid glands include mumps, bacterial infections and tumors, according to the Merck Manual Consumer Edition. The parotid glands are between the front of the ears and the jawline. They are part of a system of glands that produce saliva to help with the digestion of food.
In 30 to 40 percent of patients with mumps, the parotid glands swell. The swelling begins within 48 hours after the beginning of other symptoms, such as fever or headache, according to WebMD. Mumps is a viral condition more common in children than in adults. Other viral causes of swelling of these glands include the human immunodeficiency virus, cytomegalovirus, Epstein-Barr virus and Coxsackievirus.
Swelling due to bacterial infections generally affects one of the parotid glands but not the other. These infections are sometimes due to bacteria that are a part of the normal flora of the mouth; however, staph bacteria can also infect the glands. Malnutrition and dehydration increase the chances of a parotid infection indicates WebMD.
Tumors cause the parotid gland to swell. While cancerous and noncancerous tumors are possible in this region, benign ones are the most common, reports WebMD. Warthin's tumor and pleomorphic adenomas are the two most common types.