Cellulitis of the head and neck region is a condition caused by an infection, often of odontogenic origin, resulting in edema and acute inflammation that spreads through the fascial planes of the soft tissues and can also spread to the facial bones. Soft tissue infections of the mouth floor can be caused by pericoronitis, periodontitis, complications during recent dental work, or by upper respiratory infections. Infections of the second and third lower molars are the usual culprits. The most common causative pathogens are beta-hemolytic and aerobic streptococci, and rarer pathogens include Staphylococcus, Preptostreptococcus, Fusobacterium, Bacteroides, Prevotella, Capnocytophaga, and Haemophilus.

Pain and swelling are the main complaints, and systemic symptoms such as fever, malaise, and chills are common. Ludwig's angina is the term used when a gangrenous cellulitis spreads to the submandibular, submental, and sublingual spaces.

With cellulitis of the head and neck region, patients generally report a history of a toothache that is recurrent or relapsing over weeks to months; there may also be a history of trismus. Over days, painful and tender swelling develops on the face, overlying the area of the painful tooth. Cellulitis may also result from a penetrating injury to the soft tissues, with ensuing inflammation and infection. In patients with diabetes mellitus and in immunosuppressed individuals, the infection can spread to cause large abscesses, necrosis, and dissemination into the blood. Patients who are immunocompromised are particularly prone to the development of this condition. If not treated quickly, infections of the mouth floor and deep neck can be fatal, from sepsis and airway obstruction. Complications from oral cellulitis can include orbital infections / orbital cellulitis, cavernous sinus thrombosis, mediastinitis, pneumonia, sepsis, facial scarring, and loss of teeth.

Recently published reports indicate an increase in the incidence of methicillin-resistant Staphylococcus aureus (MRSA)-associated head and neck infections, particularly in the pediatric population.