Black fingernails can be a cause for concern. While some instances of nail discoloration are harmless and resolve on their own, others can signal a more serious underlying health issue. Understanding the causes helps recognize when medical attention is necessary. This discoloration, medically termed melanonychia, can appear as spots, streaks, or even cover the entire nail.
Everyday Explanations for Black Fingernails
A common and less serious cause of a black fingernail is a subungual hematoma. This occurs when trauma, such as a crushing injury or dropping a heavy object on the nail, causes blood vessels beneath the nail to rupture. The blood then pools under the nail plate, leading to dark red, purple, or black discoloration. This often causes throbbing pain due to trapped blood pressure and typically grows out with the nail.
External factors can also lead to black staining on the nail surface. Dyes from clothing, inks, chemicals, tar, or even certain foods can leave dark marks on the nail plate. Unlike a subungual hematoma where the discoloration is beneath the nail, these stains are on the nail itself and may be cleaned off or will eventually grow out with the nail. These stains are generally harmless.
Underlying Health Concerns
Beyond everyday occurrences, black fingernails can indicate more significant health issues. Fungal infections, known as onychomycosis, can cause black or dark brown nail discoloration. These infections often make the nail thickened, brittle, or cause it to lift from the nail bed. While typically yellow or white, some fungi produce melanin, leading to darker discoloration.
Bacterial infections may also appear as dark spots or streaks. These infections might be accompanied by pus, inflammation, or a foul odor. For instance, certain bacterial infections can cause a greenish-black discoloration.
A more serious cause of a black streak under the nail is subungual melanoma, a type of skin cancer. It appears as a black or dark brown streak, often running vertically from the cuticle to the nail tip. Unlike a bruise, this streak may widen, change in color intensity, or involve the surrounding skin, a sign known as Hutchinson’s sign. Early detection is important for successful treatment.
Certain medications can also induce nail discoloration as a side effect. Chemotherapy drugs, for example, cause black or brown nail discoloration. Other medications, such as some antimalarials or minocycline, a type of antibiotic, can also cause nail pigmentation. Discoloration can appear as longitudinal or transverse bands, or be diffuse across the nail.
Black fingernails can also be a symptom of underlying systemic diseases. Conditions such as Addison’s disease, Cushing’s syndrome, or certain autoimmune disorders can lead to nail discoloration. Nutritional deficiencies, particularly of folate and vitamin B12, have also been linked to melanonychia.
When to Seek Medical Attention
Seek medical evaluation for any black fingernail discoloration that appears without a clear cause, such as an injury. Medical attention is advised if the discoloration is growing or changing in size, shape, or color. Other concerning signs include pain, swelling, or pus.
If the black discoloration involves multiple nails or extends to the skin surrounding the nail, known as Hutchinson’s sign, a medical consultation is particularly important. Any persistent black discoloration that does not resolve as the nail grows out, or lacks known trauma, warrants professional assessment.
What to Expect at the Doctor’s Office
A doctor’s consultation for black fingernails typically begins with a thorough medical history. They will ask about the discoloration’s onset, associated symptoms like pain or swelling, and any recent trauma or chemical exposure. A physical examination of the affected nail and surrounding skin will follow, often using a magnified view.
Diagnostic tests may be recommended to determine the cause. This could involve dermoscopy, a non-invasive technique using a specialized magnifying device to examine the nail and skin. For suspected fungal infections, a nail clipping may be taken for a fungal culture to identify the specific fungus. If melanoma is a concern, a nail biopsy, involving a small tissue sample for microscopic examination, might be performed.
For a painful subungual hematoma, the doctor may drain trapped blood by making a small hole in the nail, a procedure called trephination, to relieve pressure. Fungal infections are treated with antifungal medications, either oral or topical. If subungual melanoma is diagnosed, surgical removal is often necessary.