Black spots appearing on fingernails or toenails can be a cause for concern. While alarming, these spots can arise from a wide range of factors. Many causes are harmless and temporary, yet some indicate underlying conditions that warrant medical attention. Understanding these potential reasons helps in discerning when professional evaluation is advisable.
Common Benign Causes
Trauma is a frequent cause of black spots under the nail, leading to a subungual hematoma. This occurs when an injury, such as stubbing a toe or dropping an object on a finger, causes blood vessels beneath the nail plate to rupture. The trapped blood pools and darkens as it clots, appearing as a black or dark blue spot. This discoloration typically resolves as the nail grows, pushing the discolored area forward.
Another common benign cause is splinter hemorrhages, which appear as thin, reddish-brown or black lines resembling splinters under the nail. These are small streaks of blood resulting from minor damage to the tiny capillaries in the nail bed. They are most often caused by minor trauma, such as repetitive small impacts. In most cases, they are isolated events related to everyday activities and are not indicative of serious health issues.
Fungal infections, medically termed onychomycosis, can also lead to discoloration, including dark spots or streaks. Certain types of fungi can produce pigments that stain the nail plate directly, or discoloration can result from debris accumulating under the nail as the infection progresses. This debris can appear dark brown or black. Fungal infections often cause the nail to thicken, become brittle, or lift from the nail bed, distinguishing them from simple bruising.
Pigmented Lesions and Malignancies
Pigmented lesions, such as subungual nevi, are essentially moles that develop under the nail. These benign growths of pigment-producing cells can appear as stable, dark streaks or spots that do not change significantly over time. While most nevi are harmless, their presence can sometimes be confused with more serious conditions. A nevus typically presents as a uniform band of color that grows slowly with the nail.
Melanonychia is a broader term describing any brown or black discoloration of the nail, often appearing as a longitudinal streak. This condition arises from increased melanin production by pigment cells in the nail matrix. It can be a benign finding, especially in individuals with darker skin tones (racial melanonychia), or it can be induced by certain medications or systemic diseases. However, melanonychia can also be a sign of a more concerning process.
The most serious, though less common, cause of black nail discoloration is subungual melanoma, a type of skin cancer originating in the nail matrix. This malignancy often presents as a dark, widening, and irregularly shaped streak that may change in color or size over time. A particular warning sign, known as Hutchinson’s sign, occurs when the pigment extends from the nail plate onto the surrounding skin of the cuticle or nail fold. Early detection of subungual melanoma is important for successful treatment, emphasizing the need for prompt evaluation of suspicious changes.
Other Underlying Factors
Certain medications can induce nail discoloration, leading to the appearance of black spots or streaks. Drugs such as some chemotherapy agents, antimalarials, and tetracycline antibiotics are known to cause hyperpigmentation of the nail plate or nail bed. This discoloration is typically a side effect of the medication and usually resolves after the drug is discontinued.
Systemic conditions, while less common, can also manifest with changes in nail pigmentation. For example, endocrine disorders like Addison’s disease, which affects the adrenal glands, can lead to increased melanin production and diffuse nail pigmentation. Chronic kidney disease and certain heavy metal toxicities have also been reported to cause nail discoloration. These systemic causes are typically accompanied by other symptoms related to the underlying condition.
External factors can also contribute to black nail spots through direct staining. Exposure to certain chemicals, such as silver nitrate used in some medical treatments or hair dyes, can temporarily stain the nail plate a dark color. This type of discoloration is usually superficial and will grow out with the nail. It is important to consider recent exposures when evaluating new nail discoloration.
When to Consult a Professional
It is advisable to consult a healthcare professional, especially a dermatologist, if you observe certain characteristics or changes in a black spot on your nail. Seek evaluation if the spot or streak appears without any known trauma, as this raises suspicion for other causes. A professional can help distinguish between benign conditions and more serious concerns.
Changes in the size, shape, or color of an existing spot warrant prompt medical attention. A dark streak that extends onto the skin surrounding the nail, particularly the cuticle or nail fold, known as Hutchinson’s sign, is a warning sign that needs immediate assessment. This specific sign is often associated with subungual melanoma.
Other concerning features include the presence of multiple dark spots or streaks, particularly if they appear suddenly or are rapidly changing. Any associated symptoms, such as pain, bleeding, or a sensation of the nail lifting from the nail bed, also indicate the need for professional examination. If you have persistent concern or uncertainty about any nail discoloration, consulting a healthcare provider is always the appropriate course of action.