Causes of a lump under the tongue include salivary gland diseases, such as sialolithiasis, sialadenitis, viral infections and cysts, states Cedars-Sinai Medical Center. These afflictions are located in the ducts of the salivary glands. Other conditions causing lumps under the tongue include Sjögren's syndrome, sialadenosis and tumors.
Sialolithiasis occurs when small salivary stones made of calcium form in the glands, which may block the ducts. While sialolithiasis doesn't always produce symptoms, pain, swelling and an infection may develop when the duct becomes blocked, according to Cedars-Sinai Medical Center. Cysts can develop as a result of sialolithiasis, as well as after viral infections, injuries or tumors.
Sjögren's syndrome occurs when white blood cells injure the moisture-producing salivary glands, tear-producing glands, and even the sweat and oil glands. This syndrome is a chronic condition usually seen in middle-age women and in people with rheumatoid arthritis, lupus, scleroderma and polymyositis, states the Cedars-Sinai Medical Center.
One of the three major parts of the salivary glands, the sublingual glands, are under the tongue, and infection of, or injury to, these glands can cause lumps to appear under the tongue, states WebMD. Though tumors in this region of the mouth can be cancerous, they are commonly found to be benign.