The appearance of a black spot on the inside of the cheek, known medically as the buccal mucosa, often causes immediate concern. This delicate lining of the mouth is a common site for pigmented lesions, which can range widely in origin from completely harmless anatomical variations to indicators of a systemic condition or, rarely, a serious disease. While the vast majority of these dark spots are benign, any new, changing, or unexplained discoloration within the mouth warrants professional assessment. Understanding the various causes helps to demystify this finding, but a definitive diagnosis requires evaluation by a dental professional or an oral pathologist.
Benign Pigmentation and Anatomical Features
Many instances of dark spots on the inner cheek are simply the result of natural processes or common benign growths. Physiological pigmentation is the most frequent cause of diffuse discoloration, resulting from the normal production and deposition of melanin. This coloring is more common in individuals with darker skin tones, such as those of African, Asian, or Mediterranean descent, and typically presents as symmetrical, brownish patches.
Oral nevi, essentially moles inside the mouth, are another common benign finding. These lesions are small, usually less than one centimeter in diameter, and often appear as a stable, well-defined brown or bluish macule. Like skin moles, oral nevi are collections of melanocyte cells that typically cease growth once they reach a certain size.
A less common condition is oral melanoacanthoma, which often presents on the buccal mucosa. This appears as a rapidly enlarging, dark brown or black patch or plaque. Unlike malignant lesions, melanoacanthoma is considered a reactive process, frequently linked to local irritation or minor trauma. The rapid onset of this lesion often causes alarm, but it is harmless and may even spontaneously regress once the source of irritation is removed.
Pigmentation Caused by Trauma or Foreign Material
Some of the most distinct black or dark blue spots in the oral cavity are caused by the accidental introduction of foreign materials or localized injury. The amalgam tattoo is the most frequent localized pigmented lesion stemming from an external source. It presents as a flat, asymptomatic, dark gray, blue, or black macule near a tooth that has, or previously had, an amalgam filling.
This pigmentation occurs when tiny particles of dental amalgam become embedded in the soft tissues during a dental procedure. These metallic particles leach into the surrounding connective tissue, permanently staining the area. While an X-ray may sometimes reveal larger metal fragments, the lack of radiographic evidence does not rule out the diagnosis, as particles can be too fine or dispersed to be visible.
Another traumatic cause is a hematoma, or bruise, resulting from blood pooling under the surface tissue after accidentally biting the cheek or following a dental procedure. A hematoma appears as a dark red, purple, or black area and should resolve completely within two weeks as the body reabsorbs the pooled blood. Post-inflammatory hyperpigmentation can also occur, leaving a temporary dark patch after a minor injury heals.
Systemic Conditions and Medication Side Effects
In rare instances, a black spot can be a manifestation of an underlying health issue or a reaction to medication. Certain pharmaceutical agents induce hyperpigmentation in the mouth and on the skin. The antibiotic minocycline, used for long-term conditions like acne, can cause a blue-gray or muddy brown discoloration of the oral mucosa, often appearing after extended use.
Endocrine disorders can also lead to diffuse pigmentation. Addison’s disease, resulting from the adrenal glands not producing enough hormones, often presents with generalized darkening of the skin and oral tissues due to increased melanocyte stimulation. The pigmentation is typically diffuse and involves multiple sites, not just an isolated spot.
Genetic syndromes may also be responsible for oral pigmentation. Peutz-Jeghers syndrome is characterized by the presence of dark brown or black spots, resembling freckles, on the lips, around the mouth, and on the buccal mucosa. These spots often occur in conjunction with polyps in the gastrointestinal tract. While the spots themselves are benign, they serve as a marker for the syndrome, which carries an increased risk for various cancers.
Recognizing Warning Signs and Next Steps
The most serious, though uncommon, cause of a dark spot is oral mucosal melanoma, which requires prompt attention. The modified ABCDE rule, originally designed for skin lesions, serves as a useful guide for early detection. The rule highlights five characteristics of concern:
- Asymmetry: One half does not match the other.
- Border: The edges are irregular, notched, or blurred.
- Color: There is variation within the spot, such as multiple shades of brown, black, blue, or red.
- Diameter: The spot is larger than six millimeters (roughly the size of a pencil eraser).
- Evolution: There is any noticeable change in the lesion’s size, shape, color, or height over time.
Any spot that is newly appearing, rapidly changing, or associated with symptoms like bleeding, pain, or a raised surface must be immediately evaluated.
Because benign lesions like amalgam tattoos and malignant lesions can look deceptively similar, a thorough professional examination is necessary. If a black spot cannot be confidently diagnosed as benign based on clinical appearance, a biopsy will be recommended to obtain a definitive tissue diagnosis. Consulting a dentist, oral surgeon, or oral pathologist is the appropriate next step for timely and accurate identification.