AbstractEndodontic cellulitis involves facial swelling which can vary from mild to severe and can occur as a primary case or a flare‐up following initial treatment of asymptomatic teeth with periapical lesions. The microbial spectrum in primary cases involves a significant mixture of anaerobic and facultative aerobic microbes, chiefly streptococci. In a previous study, cultures from flare‐up cases, utilizing the same anaerobic techniques as in primary cases, revealed an absence of obligate anaerobes and an 80 per cent incidence of facultative aerobic streptococci. These cases also revealed a significant time lapse from onset of symptoms to the cellulitis phase. No sex or age factors were noted in the primary or flare‐up cases.The purpose of this case report is to restate a traditional theory, namely, the alteration of the oxidation/reduction potential (Eh), as a major factor for endodontic cellulitis flare‐ups; to confirm the pathogenic potential of oral facultative streptococci; and that asymptomatic endodontic lesions tend to exist with mixed aerobic/anaerobic microbia