TL;DR

Key Facts

What Are They?

Pigmented lesions of the oral cavity are areas of altered mucosal colour resulting from the deposition of endogenous or exogenous pigments within the epithelium or underlying connective tissue. They represent one of the most diagnostically challenging categories in oral medicine because a wide variety of benign, reactive, and malignant conditions can produce clinically similar brown, blue, grey, or black discolouration.

Pigmentation sources in the oral cavity fall into two main categories:

• Endogenous pigments — produced within the body. The most important is melanin, synthesised by melanocytes within the basal layer of the oral epithelium. Other endogenous pigments include haemoglobin derivatives (haemosiderin, haematoidin) seen in bruising and vascular lesions, and bilirubin in jaundice.
• Exogenous pigments — introduced from outside the body. Dental materials (amalgam, graphite), heavy metals (lead, bismuth, silver), and foreign bodies can produce focal or diffuse mucosal discolouration.

Understanding the source and distribution of pigmentation — whether diffuse or focal, flat or raised, stable or changing — is the first step in building a differential diagnosis and determining which lesions require biopsy.

Why It Matters (Clinical + Exam Context)

Oral pigmented lesions matter clinically because the spectrum of diagnoses includes conditions with no treatment implications at one extreme and life-threatening malignancy at the other. The inability to reliably differentiate benign from malignant pigmentation on clinical grounds alone makes systematic assessment and selective biopsy essential skills.

Clinical Relevance

• Melanoma vs. melanotic macule: Both can present as flat, dark-brown macules on the oral mucosa. Melanoma may initially appear deceptively benign. Biopsy is the only reliable differentiator, and early diagnosis is the single most important prognostic factor in melanoma.
• Systemic associations: Multiple oral melanotic macules combined with perioral lentigines (lip spots) and intestinal polyposis define Peutz-Jeghers syndrome (STK11/LKB1 mutation) — an autosomal dominant condition requiring lifelong GI surveillance for malignancy. Diffuse bronze oral pigmentation in association with skin hyperpigmentation and systemic illness may indicate Addison disease (primary adrenocortical insufficiency), where elevated ACTH cross-stimulates melanocyte-stimulating hormone (MSH) receptors.
• Drug-induced pigmentation: Several medications cause diffuse oral mucosal pigmentation — antimalarials (hydroxychloroquine, chloroquine), minocycline, zidovudine (AZT), and some chemotherapy agents. A thorough medication history is essential when assessing any case of new-onset oral pigmentation.
• HIV and melanosis: Diffuse oral melanosis is a recognised finding in HIV-positive patients, related to adrenocortical dysfunction, drug effects (especially AZT), or direct mucosal effects of the virus.

Endogenous Pigmented Lesions

Physiological (Racial) Melanosis

The most common cause of oral pigmentation worldwide, physiological melanosis represents normal variation in melanin production. It is most prevalent in individuals of African, Asian, and Mediterranean descent but can occur in any ethnicity. The pigmentation is diffuse, bilaterally symmetrical, flat, and stable. The attached gingiva is the most common site, followed by the hard palate and buccal mucosa. No treatment is required; the clinical importance lies in recognising this normal variant and avoiding unnecessary investigation or patient alarm. Any asymmetry, rapid change, or raised component should prompt biopsy.

Melanotic Macule (Focal Oral Melanosis)

The melanotic macule is the most common localised melanin-pigmented lesion of the oral cavity. It is a completely flat (macular), well-defined, uniformly pigmented lesion measuring typically 1–8 mm, brown to dark brown in colour. The vermilion border of the lower lip is the most frequent site, followed by the gingiva, buccal mucosa, and palate. It represents a focal increase in melanin production by a normal number of melanocytes — not a proliferation of melanocytes. Histologically there is increased melanin in the basal cell layer with minimal to no increase in melanocyte number. Treatment is excisional biopsy both to establish the diagnosis and to provide definitive management. Recurrence is uncommon.

Melanocytic Naevi (Moles)

Intraoral melanocytic naevi are uncommon but are important because they must be distinguished from melanoma. They are well-defined, slightly raised (or occasionally flat), brown to dark brown lesions most commonly found on the hard palate and buccal mucosa. Four histological subtypes parallel those in skin: intramucosal (most common intraoral type — naevus cells confined to connective tissue), junctional, compound, and blue naevus (heavily pigmented spindle cells deep in the connective tissue, appearing steel-blue clinically). All intraoral naevi should be excised and submitted for histopathological examination because of the risk of misdiagnosing melanoma as a benign naevus.

Lentigo and Peutz-Jeghers Syndrome

Oral lentigines are flat, brown macules with increased numbers of melanocytes at the epithelial-connective tissue junction (unlike the melanotic macule where melanocyte numbers are normal). When multiple perioral and intraoral lentigines occur in a young patient, Peutz-Jeghers syndrome must be excluded. This autosomal dominant condition is caused by mutations in the STK11 (also called LKB1) gene and is characterised by perioral and mucosal lentigines combined with gastrointestinal hamartomatous polyps. The polyps carry a significant cumulative risk of malignancy (particularly small bowel and colorectal carcinoma), making referral for GI surveillance essential.

Addison Disease Pigmentation

Addison disease (primary adrenocortical insufficiency) causes diffuse hyperpigmentation of the skin and oral mucosa due to elevated levels of adrenocorticotrophic hormone (ACTH), which cross-reacts with melanocortin receptors on melanocytes. Oral manifestations appear as diffuse, patchy brown pigmentation of the buccal mucosa, gingiva, lips, and tongue — typically symmetrical. The pigmentation often predates diagnosis of the systemic condition, making the oral clinician’s recognition potentially life-saving. Associated features include fatigue, weight loss, hypotension, and salt craving. Urgent medical referral is required.

Haemosiderin Pigmentation

Localised areas of brown pigmentation can result from haemosiderin deposition following extravasation of red blood cells into the mucosa. Haemosiderin is a degradation product of haemoglobin released from lysed erythrocytes. It appears histologically as golden-brown granules within macrophages (siderophages) and stains positively with Perls’ Prussian blue. Clinically this produces brown or orange-brown macules, often following trauma, repeated small haemorrhages (as in vascular malformations), or in association with peripheral giant cell granuloma. Unlike melanin, haemosiderin does not fade appreciably with time.

Exogenous Pigmented Lesions

Amalgam Tattoo

The amalgam tattoo (focal argyrosis) is the most common exogenous pigmented lesion in the oral cavity. It results from the iatrogenic implantation of amalgam particles into the oral soft tissues during dental procedures — placement or removal of amalgam restorations, tooth extraction, or surgical procedures near amalgam restorations. The lesion appears as a flat, grey-blue macule that is entirely asymptomatic and does not change over time. The gingiva and alveolar mucosa are the most frequent sites. Radiographic identification of radiopaque amalgam particles within the soft tissue on periapical or bite-wing radiographs confirms the diagnosis without biopsy. If no radiopacity is visible, biopsy is recommended to exclude blue naevus, melanoma, or vascular lesion. Histologically, black or brown metallic particles are distributed along collagen fibres and around blood vessels. No treatment is required unless cosmesis is a concern.

Graphite Tattoo

Pencil graphite accidentally implanted into the oral mucosa — most often the hard palate in children who fall while holding a pencil in their mouth — produces a similar grey-blue focal pigmentation. The particles are non-reactive and the lesion is stable. Biopsy confirms graphite rather than amalgam on histological examination.

Heavy Metal Pigmentation

Chronic systemic exposure to heavy metals can produce a characteristic line of pigmentation along the gingival margin:

• Lead (Burton’s line): A blue-black line along the free gingival margin, caused by lead sulphide deposition. Associated with systemic lead poisoning (plumbism).
• Bismuth: Similar gingival line, historically seen with bismuth-based medication for syphilis.
• Mercury: Also produces a gingival blue-black line; seen with chronic mercury exposure.

These presentations are rare in the modern era due to improved occupational safety standards and changes in medical treatment, but they remain important for examination purposes and in occupational health contexts.

Drug-Induced Pigmentation

A range of medications can cause diffuse or patchy oral mucosal pigmentation by stimulating melanin production, depositing drug metabolites in tissues, or causing haemosiderin accumulation:

• Antimalarials (hydroxychloroquine, chloroquine): Hard palate pigmentation; melanin-like deposits.
• Minocycline: Blue-grey discolouration of the hard palate bone visible through the mucosa; also stains the teeth blue-grey.
• Zidovudine (AZT): Diffuse oral melanosis, particularly in HIV-positive patients.
• Clofazimine: Red-brown discolouration; used in leprosy treatment.

Oral Malignant Melanoma

Oral malignant melanoma (OMM) is a rare but highly aggressive neoplasm arising from malignant transformation of melanocytes within the oral mucosa. It accounts for approximately 0.5% of all oral malignancies but carries a disproportionately poor prognosis. The hard palate and maxillary gingiva account for more than 80% of cases; the mandibular gingiva and buccal mucosa are less commonly involved.

Clinical Features

OMM can present as a brown, black, red, white, or mixed-colour lesion. The classic presentation is an irregular, asymmetric pigmented macule or plaque with variegated colour, indistinct borders, and associated areas of ulceration, bleeding, or swelling. However, amelanotic (unpigmented) variants occur and are particularly treacherous because the absence of pigmentation may delay diagnosis. Approximately one-third of cases are preceded by a history of pre-existing oral pigmentation for months to years before frank malignancy develops.

Diagnosis and Staging

Diagnosis is confirmed by incisional biopsy and histopathological examination with immunohistochemical staining for melanocytic markers (S-100 protein, HMB-45, Melan-A/MART-1, SOX10). CT and MRI of the head and neck establish local extent and regional nodal involvement. PET-CT is used for distant staging. Unlike cutaneous melanoma, no universally accepted staging system specific to OMM exists; most centres adapt the AJCC TNM system for mucosal melanoma.

Treatment and Prognosis

Wide surgical excision with clear margins is the primary treatment. Due to the rich lymphatic drainage of the oral cavity, regional lymph node dissection or sentinel node biopsy is commonly performed. Radiation therapy reduces local recurrence but does not improve overall survival. Systemic therapy with immune checkpoint inhibitors (anti-PD-1 antibodies: pembrolizumab, nivolumab) and targeted agents (BRAF/MEK inhibitors where BRAF mutation is present) is increasingly used for metastatic or unresectable disease, showing improved outcomes over historical chemotherapy. Despite multimodal treatment, the prognosis remains poor — partly due to late clinical presentation, partly due to the biologically aggressive nature of mucosal compared to cutaneous melanoma.

Clinical Considerations

• The ABCDEs of oral pigmented lesions: Asymmetry, Border irregularity, Colour variation, Diameter >6 mm, and Evolution (change over time) are warning features borrowed from dermatology that are equally applicable to oral pigmented lesions. Any lesion meeting one or more of these criteria warrants biopsy.
• Diascopy for vascular vs. pigmented lesions: Press a glass slide firmly against the lesion. Blanching (disappearance of colour) indicates a vascular lesion (blood displaced from vessels). Persistent colour (no blanching) confirms pigment — either melanin, haemosiderin, or exogenous material — within the tissue.
• Radiology before biopsy: For any gingival or palatal pigmented lesion, a periapical radiograph should be taken before biopsy to detect amalgam particles. If radiopaque fragments are visible within the soft tissue and the clinical history is consistent, a diagnosis of amalgam tattoo can be made without biopsy.
• Medication history: Document all medications at the time of assessment. Drug-induced mucosal pigmentation is common, typically reversible on drug cessation, and spares the need for invasive investigation if correctly identified.
• Systemic screening: Multiple oral lentigines — especially in a young patient with perioral pigmentation — must trigger referral for Peutz-Jeghers syndrome screening (GI endoscopy). Diffuse bronze pigmentation with systemic symptoms must trigger Addison disease workup (serum cortisol, ACTH stimulation test).

Common Mistakes & Misconceptions

• Misconception: “Stable pigmentation is always benign.”
  Correction: Oral melanoma can have a prolonged early (radial growth) phase during which it appears clinically stable and may be mistaken for a benign melanotic macule. Stability alone does not guarantee benignity. Biopsy of any unexplained discrete oral pigmentation is the only reliable safeguard.
• Misconception: “Amalgam tattoo always appears radiopaque on X-ray.”
  Correction: Only amalgam particles large enough to be radiographically detectable will appear radiopaque. Fine amalgam particles — particularly from polishing — may not be visible on radiograph. When no radiopacity is seen but the clinical diagnosis of amalgam tattoo is suspected, biopsy is required to exclude melanoma.
• Misconception: “Physiological melanosis is only seen in Black patients.”
  Correction: Physiological oral melanosis occurs across all ethnicities but is more prevalent and more prominent in individuals with darker skin tones. It can occur in patients of any racial background, including those with light complexions.
• Misconception: “Oral melanoma always presents as a pigmented lesion.”
  Correction: Amelanotic oral melanoma lacks visible pigmentation and may present as a pink, red, or flesh-coloured swelling or ulceration. A high index of suspicion must be maintained for any unexplained oral mucosal abnormality, particularly on the hard palate or maxillary gingiva.

Related Topics

References & Sources

1. Neville BW, Damm DD, Allen CM, Chi AC. (2016). Oral and Maxillofacial Pathology, 4th ed. Elsevier.
2. Regezi JA, Sciubba JJ, Jordan RCK. (2017). Oral Pathology: Clinical Pathologic Correlations, 7th ed. Elsevier.
3. Odell EW (Ed.). (2017). Cawson’s Essentials of Oral Pathology and Oral Medicine, 9th ed. Elsevier.
4. Gondak RO, da Silva-Jorge R, Jorge J, Lopes MA, Vargas PA. (2012). Oral pigmented lesions: Clinicopathologic features and review of the literature. Medicina Oral Patología Oral y Cirugía Bucal, 17(6), e919–e924.
5. Rapidis AD, Apostolidis C, Vilos G, Valsamis S. (2003). Primary malignant melanoma of the oral mucosa. Journal of Oral and Maxillofacial Surgery, 61(9), 1132–1139.

Summary

Oral pigmented lesions encompass a broad spectrum from entirely normal physiological melanosis to the highly aggressive oral malignant melanoma. The clinical challenge lies in distinguishing these entities on the basis of distribution, colour character, stability, and associated features, while recognising that clinical assessment alone cannot reliably exclude melanoma. A systematic approach — including medication history, diascopy, radiographic screening for amalgam, systemic assessment for Addison disease and Peutz-Jeghers syndrome, and selective biopsy — is essential for safe and comprehensive management.

About the Author

Dr. Andries Smith

Founder, Dental Panda

Dr. Andries Smith founded Dental Panda in 2020. As an immigrant to the United States, he had to take the INBDE exam, even though he was practicing dentistry for over 10 years. This revealed an opportunity. Andries noticed that INBDE prep course companies were putting profit over students. With his expertise and experience in dentistry, he created free dental wiki resources for students and the general public to have access to.