The appearance of dark or “black” patches on the lips is known as lip hyperpigmentation. This discoloration occurs when there is an excess production or deposition of melanin, the natural pigment that determines color. Lip color is naturally determined by the concentration of melanin and the visibility of underlying blood vessels through the thin mucosal tissue. A sudden or gradual change in this pigmentation can signal various underlying factors, ranging from benign external habits to complex internal medical conditions. Determining the cause requires examining a person’s lifestyle, medications, and overall health status.
External and Lifestyle Contributors
The most common causes of lip darkening stem from direct exposure or chronic habits. Prolonged sun exposure, specifically ultraviolet (UV) radiation, stimulates melanocytes in the lips to produce more melanin as a protective mechanism. Because the skin of the lips is delicate, this increase in pigment becomes readily apparent. This darkening is essentially a form of sun-induced hyperpigmentation.
Another significant habit-related cause is long-term tobacco use, which leads to a distinct pattern called smoker’s melanosis. Nicotine and various chemicals in tobacco smoke stimulate melanocytes to increase melanin production, often resulting in blotchy or diffuse darkening of the lips and oral mucosa. Chronic irritation or trauma, such as habitually biting or licking, can also lead to post-inflammatory hyperpigmentation. This inflammatory response causes pigment release that settles in the healing tissue.
Furthermore, some lip pigmentation is simply physiologic, meaning it is a natural variation determined by genetics and ethnicity. Individuals with darker complexions often have naturally higher melanin levels. This can manifest as a darker, uniform lip color that is completely normal and requires no medical concern.
Systemic Medical Conditions
When lip darkening is not explained by external factors, it may signal an internal systemic disease. One condition is Addison’s disease, where the adrenal glands do not produce sufficient cortisol. This lack of cortisol triggers the pituitary gland to release excess adrenocorticotropic hormone (ACTH) in an attempt to stimulate the failing adrenals.
ACTH shares a precursor molecule with melanocyte-stimulating hormone (MSH). Therefore, high ACTH levels inadvertently stimulate melanin production in the skin and mucous membranes. This hormonal effect causes characteristic blue-black or brown patches on the lips, gums, and oral lining, often appearing months or years before other symptoms of the disease.
Another distinct cause is Peutz-Jeghers Syndrome (PJS), a rare inherited disorder linked to a mutation in the STK11 gene. PJS is characterized by small, dark brown to blue-black macules (1 to 5 millimeters) on the lips and around the mouth. These spots are typically present in childhood and are associated with hamartomatous polyps throughout the gastrointestinal tract, significantly increasing the lifetime risk for various cancers. Other internal issues contributing to discoloration include hemochromatosis, a disorder of iron metabolism, and severe vitamin B12 deficiency.
Drug-Induced Pigmentation
A number of prescription medications can cause lip hyperpigmentation as a side effect by accumulating in the mucosal tissues. The antibiotic minocycline, frequently used for long-term treatment of acne and rosacea, is a well-known culprit. This medication can cause a blue-black, blue-grey, or muddy brown discoloration in the lips and gums, sometimes after just a few months of use.
The mechanism involves the deposition of drug metabolites or complexes directly into the dermal layer. Anti-malarial drugs (like chloroquine and hydroxychloroquine), some chemotherapy agents, antipsychotic medications, and anti-retroviral therapies are also implicated. Medication-induced discoloration is often dose-dependent and may partially or fully reverse once the offending drug is discontinued, although the process can take an extended period.
Next Steps Diagnosis and Management
Any new, sudden, or unexplained darkening of the lips warrants consultation with a healthcare professional, such as a dermatologist. Diagnosis begins with a thorough medical history focusing on the onset, associated symptoms, and recent changes in medication or lifestyle. A physical examination determines the pattern, color, and location of the pigment, offering clues about the underlying cause.
If a systemic cause like Addison’s disease is suspected, blood tests check hormone levels, such as cortisol and ACTH. For distinct spots or macules associated with gastrointestinal symptoms, genetic testing or endoscopic evaluation may be necessary to rule out conditions like Peutz-Jeghers Syndrome. In ambiguous cases, a small tissue sample, or biopsy, may be taken to confirm the diagnosis.
Management depends on accurately identifying the root cause of the discoloration. If a medication is responsible, switching to an alternative drug may lead to the fading of the pigmentation over time. When an underlying disease like Addison’s is identified, treating that condition with appropriate hormonal therapy is the priority, which often leads to the lightening of the mucosal pigment. For benign, cosmetic concerns, options include topical lightening agents, chemical peels, and laser therapy.