A brown spot on the lip is a sign of lip hyperpigmentation, a common condition where melanocytes, the cells responsible for producing color, generate excess melanin. This overproduction leads to localized darkening of the lip tissue. While this discoloration is frequently a benign cosmetic concern, the lip area is sensitive and can be affected by a wide range of factors. Because the causes vary from simple sun exposure to systemic changes or distinct growths, a definitive diagnosis requires professional evaluation by a healthcare provider or dermatologist.
Pigmentation Due to Sun Exposure and Inflammation
The delicate skin on the lips lacks natural protection mechanisms, making it highly susceptible to damage from ultraviolet (UV) radiation. Chronic sun exposure is the primary driver for solar lentigines, commonly known as sun spots, which appear as well-defined, flat patches ranging from light yellow-brown to dark brown or black. Solar lentigines involve an increase in the number of melanocytes and persist year-round, unlike simple freckles.
Another common cause of darkening is post-inflammatory hyperpigmentation (PIH), which occurs when the skin responds to injury or irritation by depositing excess melanin as it heals. Trauma from lip-biting, persistent dryness or chapping, or the inflammation caused by cold sores can all trigger this process.
Discoloration may also result from allergic contact dermatitis, where the lip reacts to ingredients in products such as lipsticks, toothpastes, or lip balms. The resulting inflammation leads to temporary darkening that can persist for months after the irritant is removed. Furthermore, the heat and chemicals from smoking are sources of chronic irritation that stimulate melanocytes, often resulting in an uneven, blotchy appearance.
Hormonal and Medication-Related Pigmentation
Systemic changes, particularly hormonal fluctuations, can lead to lip pigmentation. Melasma is a common disorder associated with increased levels of estrogen and progesterone, which stimulate melanin production. This condition presents as symmetrical, grayish-brown patches often found on the cheeks, forehead, and upper lip, and is sometimes called the “mask of pregnancy.”
Melasma can also be triggered or exacerbated by hormonal contraceptives. Thyroid dysfunction, specifically hypothyroidism, has also been linked to an increased likelihood of developing melasma.
Certain medications can cause pigment deposition in the oral tissues, including the lips, known as drug-induced pigmentation. Common culprits include antimalarials like chloroquine, some antibiotics such as minocycline, and specific chemotherapy agents. This occurs either by the drug accumulating in the tissue or by stimulating melanocytes to produce more pigment.
Vascular and Mole-Like Spots
Not all dark spots are caused by melanin; some represent collections of blood vessels or benign skin growths. Venous lakes frequently appear on the lower lip due to sun damage. These spots are typically soft, compressible nodules that appear dark blue, purple, or almost black because they are filled with pooled blood in a dilated vein.
A simple test can often differentiate a venous lake from a true pigmented lesion: pressing gently on the spot may cause it to temporarily lighten or flatten. Pigmented nevi, or common moles, are also frequent occurrences on the lips and are stable clusters of melanocytes. These moles are usually stable, uniform in color and shape, and have been present for a long period without changing.
Identifying Signs of Concern and Medical Evaluation
While most brown spots on the lip are benign, any new or changing spot should be promptly evaluated by a dermatologist to rule out a serious condition like melanoma. The ABCDE rule, typically used for skin checks, is applied to lip lesions as well.
The key signs to monitor include:
- Asymmetry, where one half of the spot does not match the other.
- Border irregularity, meaning the edges are ragged, notched, or blurred.
- Color variation, especially if the spot contains multiple shades of brown, black, red, white, or blue.
- Diameter larger than six millimeters, roughly the size of a pencil eraser.
- Evolving, or any change in the lesion’s size, shape, color, or symptoms like itching or bleeding.
A medical evaluation often involves a thorough visual inspection, sometimes using a dermatoscope. If the diagnosis remains uncertain, a small tissue sample, or biopsy, may be taken for laboratory analysis.