What Causes Darkening of the Gum Tissue?

Darkening of the gingiva—the gum tissue surrounding the teeth—is a clinical finding that can arise from multiple underlying causes, ranging from benign physiological variations to more serious pathological conditions. Clinicians must approach this sign with careful differential diagnosis.

One common and entirely harmless explanation is melanin pigmentation, particularly prevalent among individuals with darker skin tones. This physiological hyperpigmentation results from increased activity of melanocytes in the gingival epithelium and typically presents as uniform, flat, brown-to-black patches that are asymptomatic and stable over time.

Another frequent cause is amalgam tattoo—a localized bluish-gray discoloration resulting from accidental implantation of dental amalgam particles into the gingival connective tissue during restorative procedures or tooth extractions. These lesions are usually solitary, well-circumscribed, and radiographically inert.

Less commonly, gingival melanosis may reflect systemic conditions such as Addison’s disease (primary adrenal insufficiency), where elevated adrenocorticotropic hormone (ACTH) stimulates melanocyte activity, leading to diffuse mucocutaneous hyperpigmentation—including in the oral cavity. Similarly, certain medications—including antimalarials (e.g., hydroxychloroquine), chemotherapeutic agents, and minocycline—can induce drug-related melanosis.

In rare but critical instances, persistent, irregular, or rapidly changing black gingival lesions warrant urgent evaluation for malignant melanoma. Oral melanoma accounts for less than 2% of all melanomas but carries a poor prognosis due to late diagnosis. Key red flags include asymmetry, irregular borders, color variegation, diameter greater than 6 mm, and evolving morphology—often summarized by the “ABCDE” mnemonic adapted for oral use.

Diagnosis hinges on thorough clinical examination, detailed patient history—including medication use, systemic symptoms, and lesion chronology—as well as biopsy when malignancy cannot be confidently excluded. Imaging or laboratory testing may be indicated depending on suspected etiology. Early recognition and appropriate referral ensure timely intervention and optimal outcomes.