The digastric muscle is a small, two-part muscle located beneath the chin and jawline. It consists of an anterior and a posterior belly joined by a central tendon. This muscle primarily functions to depress the mandible, helping open the mouth, and to elevate the hyoid bone during swallowing. Swelling in this area presents as tenderness or a palpable lump under the chin or along the jaw curve. While the symptom is felt in the location of the digastric muscle, the cause rarely originates there, often signaling issues with nearby immune structures or adjacent organs.
Mechanical Strain and Direct Injury
One direct cause of swelling is trauma to the muscle fibers. This occurs when the digastric muscle is physically damaged by a blow to the jaw or neck, or through intense, sudden force. Such an injury results in micro-tears in the muscle tissue, leading to localized inflammation, swelling, and sharp pain.
More commonly, swelling is a response to overuse or chronic tension, often associated with myofascial pain syndrome. Activities like prolonged, forceful singing, excessive yawning, or extended dental procedures can strain the muscle. Clenching and grinding the teeth (bruxism) also puts constant tension on the muscle, causing taut bands called trigger points to form.
This type of muscle-related swelling is acute, appearing quickly and accompanied by pain when the jaw moves, such as during talking or chewing. The pain from these trigger points can be referred, causing discomfort that feels like a toothache or ear pain. Unlike other causes of swelling, mechanical strain usually resolves within a few days or weeks with rest and anti-inflammatory measures.
Inflammation from Infection and Lymph Nodes
The most frequent reason for perceived swelling in the digastric region is the enlargement of nearby lymph nodes (lymphadenopathy). The submental and submandibular lymph nodes are situated adjacent to the digastric muscle. Since these nodes are part of the immune system, their enlargement is a sign that the body is actively fighting an infection in the head or neck.
Common infectious triggers include upper respiratory infections such as the common cold, flu, tonsillitis, or strep throat. Infections in the ear or throat cause the lymph nodes in the neck to become tender, enlarged, and easily felt under the jawline. The jugulodigastric node, specifically, lies at the posterior belly of the muscle and is a primary drain for the tonsils and pharynx.
Swollen lymph nodes due to infection are usually soft, mobile, and painful to the touch. This swelling is often accompanied by systemic symptoms like a fever, fatigue, or a sore throat, providing a strong clue to the underlying cause. Once the infection resolves, the immune response decreases, and the lymph nodes typically return to their normal size within one to two weeks.
Swelling Related to Nearby Glands and Abscesses
Structural issues in other organs near the digastric muscle can also mimic muscle swelling. The submandibular salivary gland, which rests in the area defined by the two bellies of the digastric muscle, is a common source of non-lymph node swelling. Inflammation of this gland (sialadenitis) often occurs when the duct is blocked by a small salivary stone (sialolithiasis).
A blocked salivary duct causes saliva to back up, leading to painful swelling. This swelling characteristically increases during or right after eating, when the gland is stimulated to produce more saliva. The swelling may be accompanied by a bad taste in the mouth or the discharge of pus if the blockage leads to an infection. This distinct timing helps differentiate it from muscle strain or lymph node swelling.
Furthermore, severe infections originating in the lower molars can track down into the floor of the mouth, creating a pocket of pus known as a dental abscess. This localized infection causes significant, firm swelling that pushes into the submandibular space, directly beside the digastric muscle. Less common causes include benign cysts, such as dermoid cysts, or, in rare instances, a tumor of the salivary gland, which often presents as a persistent, non-tender, and sometimes fixed lump.
Indicators for Professional Medical Care
While most instances of digastric area swelling are benign and related to common infections, certain signs indicate the need for a professional medical evaluation. Persistence is a key indicator: if the swelling lasts longer than two weeks without improvement, a doctor or dentist should be consulted. Swelling that rapidly worsens, particularly over hours or a few days, also warrants immediate attention.
Other concerning symptoms, often referred to as “red flags,” require prompt medical investigation. These include difficulty swallowing or breathing, which could signal a serious infection or mass compromising the airway. A high or persistent fever, night sweats, or unexplained weight loss accompanying the swelling are also specific signs that require prompt medical investigation. Finally, a lump that feels stone-hard, is fixed and immovable, or is not tender to the touch should be examined by a healthcare provider.