A sudden, noticeable swelling on only one side of the mouth or face signals an inflammatory or infectious process occurring locally in the head and neck region. The causes for this symptom are diverse, ranging from minor, self-limiting injuries to serious, rapidly spreading infections that require prompt medical intervention. Understanding the origin of the swelling, whether it is related to teeth, glands, or soft tissue, is the first step toward effective treatment.
Causes Originating from Teeth and Gums
The most frequent source of unilateral mouth swelling is an infection originating from a tooth or the surrounding gum tissue. A dental abscess represents a pocket of pus that forms when bacteria invade the inner pulp of a tooth, often through an untreated cavity or crack. This infectious material builds up pressure near the tooth root, eventually spreading into the soft tissues of the cheek, jaw, or neck, causing localized, firm swelling.
A periapical abscess forms at the tip of the tooth root, whereas a periodontal abscess develops in the gums alongside the root, typically as a complication of advanced gum disease. Both types of infection cause significant, throbbing pain that is often worsened when biting down or lying flat.
Another common dental culprit is pericoronitis, the inflammation of the gum tissue surrounding a partially erupted wisdom tooth. When a wisdom tooth is impacted, a flap of gum tissue can trap food debris and bacteria, leading to a localized infection. This results in swelling and tenderness in the jaw area, often making it difficult to fully open the mouth.
Issues Affecting Salivary Glands
Swelling beneath the jaw or near the ear may be linked to the major salivary glands, specifically the parotid or submandibular glands. Saliva drains into the mouth through ducts, but this flow can be obstructed by sialolithiasis, or the formation of salivary stones. These calcified deposits, which are most common in the submandibular gland, act like a blockage in the duct.
When saliva production is stimulated, such as during a meal, the obstructed gland swells painfully as the fluid is unable to drain properly. The swelling typically subsides after the meal, only to return with the next instance of eating.
An infection of the gland, known as sialadenitis, can also cause unilateral swelling, often accompanied by tenderness, redness, and the possible expression of pus. Bacterial sialadenitis typically affects only one gland and can arise if salivary flow is diminished. While viral infections, like mumps, often affect both sides, a bacterial cause is more likely for strictly unilateral symptoms.
Localized Soft Tissue Infections and Injury
Causes of unilateral swelling not related to teeth or glands often involve the soft tissues of the face. A simple, localized injury, such as biting the inside of the cheek or lip, can cause temporary swelling as the body responds to the minor trauma. This type of swelling is usually mild, resolves quickly, and is not accompanied by systemic signs of infection.
A more serious consideration is cellulitis, a rapidly spreading bacterial infection of the deeper layers of the skin and underlying subcutaneous tissues. Cellulitis often originates from an untreated dental abscess, as the infection spreads through the facial tissues. This condition presents as skin that is warm, red, exquisitely tender, and swollen with poorly defined borders.
Because the face has numerous interconnected tissue spaces, this infection can progress quickly, making it a medical emergency. A severe, localized allergic reaction to a food or insect bite can also manifest as unilateral swelling, though this is typically rapid in onset and may involve hives or itching. Cellulitis involves a deep, spreading bacterial process that requires immediate antibiotic treatment.
Warning Signs Requiring Emergency Care
Although many causes of unilateral mouth swelling are treatable by a dentist, specific symptoms indicate a severe, potentially life-threatening situation demanding immediate emergency medical attention. Any swelling that compromises the ability to breathe or swallow (dysphagia) is a red flag. This signifies that the infection is spreading into the deep spaces of the neck and potentially nearing the airway.
Other serious markers include a rapid and dramatic progression of the swelling over hours, or swelling that extends upward toward the eye socket. The presence of systemic symptoms like a high fever, chills, or general malaise suggests the infection has entered the bloodstream. An inability to fully open the mouth, termed trismus, also indicates a severe infectious process involving the jaw muscles.
These signs demonstrate that a localized infection has become a systemic threat and requires immediate intervention, often including intravenous antibiotics, to prevent complications such as sepsis or airway obstruction. The affected person should proceed directly to an emergency department.