Swollen glands under the tongue can indicate a viral or bacterial infection of the sublingual gland, according to MedlinePlus. Such infections are quite common and can be a result of poor hygiene, blocked salivary ducts, dehydration, smoking or chronic illness.
The sublingual is one of the glands that provide saliva to help with digestion and cleanse the mouth of food and bacteria. Most swollen glands stem from bacterial infections that inflame or block the salivary ducts and reduce the flow of saliva, according to Healthline. Viruses that cause mumps, HIV, flu or herpes are frequently the source of swollen glands. Other medical conditions that can affect the salivary glands are crystals or mucus that block the salivary ducts; tumors; an auto-immune disease that causes dry mouth; sarcoidosis or inflammation that occurs throughout the body; dehydration; malnutrition; radiation; and poor oral hygiene. People over 65 or those who haven't been immunized against mumps are vulnerable.
Salivary gland infections produce symptoms such as a bad taste or difficulty in fully opening the mouth; discomfort while eating; pus, dryness or pain in the mouth or face; swelling under the tongue, in the neck or on the face; or signs of infection such as fever or pain, according to Healthline.