Dark or black discoloration on the lips, known medically as lip hyperpigmentation, can be concerning, especially for non-smokers. This condition involves the excessive deposition of melanin, the natural pigment that gives color to skin, hair, and eyes, within the lip tissue. While often a benign cosmetic issue, lip darkening can be a symptom of various underlying causes. Understanding the cause is the first step in addressing this common dermatological finding.
Physiological and Environmental Factors
Lip darkening is often related to an individual’s natural biology or their interaction with the immediate environment. For many people, a darker lip shade is simply a reflection of their genetic background, known as physiologic pigmentation. Individuals with darker skin tones naturally produce more melanin, which can lead to a uniform, benign darkening of the lips and oral mucosa that is present from childhood or young adulthood.
The thin skin of the lips is particularly vulnerable to external irritants and trauma, which can lead to a condition called post-inflammatory hyperpigmentation. This occurs when inflammation from an injury, allergic reaction, or chronic irritation triggers melanocytes to produce and deposit excess pigment. Habits like lip licking, biting, or picking, along with chronic dryness or irritation from certain lip care products or toothpaste, can cause this localized inflammation and subsequent darkening.
Exposure to ultraviolet (UV) radiation from the sun is a primary trigger for hyperpigmentation on the lips, just as it is on the rest of the skin. UV rays stimulate melanocytes to increase melanin production as a protective response, leading to darkening of the lips. Allergic contact dermatitis from ingredients in cosmetics, lip balms, or even dental materials can also provoke an inflammatory response, depositing melanin in the affected area.
Medication-Induced Lip Darkening
Certain pharmacological agents can cause hyperpigmentation of the skin and mucous membranes, including the lips, as a side effect. This type of discoloration is caused by either the medication itself or its metabolic byproducts accumulating in the tissue. The tetracycline class of antibiotics, particularly minocycline, is well-known for causing blue-gray or brown pigmentation, which can affect the oral mucosa and lips, often appearing after large cumulative doses or long-term use.
Antimalarial drugs, such as chloroquine and hydroxychloroquine, are also implicated in causing pigmentary changes. The drug metabolites can deposit in the tissue, leading to a slate-colored or dark pigmentation that may appear on the lips and hard palate. Other medications implicated include certain chemotherapy agents, antipsychotic drugs like phenothiazines, and some anti-retroviral agents.
The discoloration from these drugs is generally a cosmetic side effect, not an indication of toxicity, but it often reverses slowly after the medication is discontinued. Exposure to heavy metals, sometimes found in certain older cosmetics or supplements, can also lead to hyperpigmentation due to the deposition of the metallic substances in the lips.
Systemic Diseases Causing Oral Pigmentation
In rare instances, lip darkening can be a visible manifestation of an underlying systemic medical condition. Addison’s disease, a form of primary adrenal insufficiency, is a notable example where hyperpigmentation occurs due to hormonal changes. The adrenal glands fail to produce enough cortisol, which leads to a compensatory increase in the pituitary hormone adrenocorticotropic hormone (ACTH).
ACTH shares a precursor molecule with melanocyte-stimulating hormone (MSH). The high ACTH levels drive up MSH, which stimulates melanin production. This results in generalized skin darkening, with a predilection for sun-exposed areas, skin folds, scars, and the oral mucosa, including the lips. Other symptoms like profound fatigue, weight loss, and low blood pressure accompany the pigmentation in Addison’s disease.
Peutz-Jeghers Syndrome (PJS) is a rare genetic disorder characterized by the development of non-cancerous polyps throughout the gastrointestinal tract. PJS is associated with small, dark brown or black spots, resembling freckles, that primarily appear on the lips, the lining of the mouth, and the skin around the eyes and nostrils. The presence of these spots, which often appear in childhood, is an important diagnostic clue due to the increased lifetime risk of various cancers linked to the syndrome.
Laugier-Hunziker Syndrome (LHS) is a rare, acquired condition that causes small, dark brown to black spots on the lips and the inside of the mouth. Unlike PJS and Addison’s disease, LHS is not associated with any underlying systemic pathology or malignant potential. The macules are typically a few millimeters in size and can sometimes be accompanied by dark, longitudinal streaks on the nails.
Determining When to Seek Medical Attention
While most cases of lip darkening are harmless, consult a healthcare provider, such as a dermatologist, if the pigmentation is a new development or is causing concern. Medical attention is warranted if the dark spots appear suddenly, change rapidly in size, shape, or color, or are asymmetrical. Discoloration accompanied by systemic symptoms—such as unexplained weight loss, chronic fatigue, gastrointestinal issues, or significant changes in blood pressure—requires immediate medical evaluation.
The diagnostic process begins with a thorough review of the patient’s medical history, including all current and past medications, and a detailed physical examination of the lips, oral cavity, and skin. A doctor may order blood tests to check hormone levels, such as those related to adrenal function, or to assess for nutritional deficiencies. In some instances, a small tissue sample, or biopsy, of the pigmented area may be taken to examine the cells and rule out more serious conditions like melanoma.