Problems with Nail Pigment: 3 Cases of a Black Nail

Pigmented nails can prompt patient anxiety, particularly if the discoloration appears suddenly. That very often happens on a Friday at about noon, Boni Elewski, MD, joked with the audience at the 2025 Midwinter Clinical Hawaii Dermatology Conference, held February 15-29, 2025, on the Big Island, Waikoloa Village, HI. The patient asks to be seen urgently and is sometimes fearing the worst – that the darkened appearance signals melanoma.

In her presentation, Nailing the Difficult to Treat Nail Disorders, Elewski shared several real-world cases to illustrate diagnostic strategies.

Trauma-induced subungual hematomas are the most common cause of acute black nails. Elewski described a patient who arrived with the second toe on one foot obviously black. When she showed the image to the audience, she pointed out that this patient had a Morton’s toe—the longest of the 5 on that foot, making it far more susceptible to trauma during daily activity. "Get out your dermatoscope," Elewski advised, which was the strategy she took and that confirmed the subungual hematoma diagnosis. If the patient is still upset, “you can do a guaiac test to confirm it's blood."

Infections, including Pseudomonas and Candida, can also cause black discoloration. The image showed a toenail that was very dark green, “so dark green that it does look black,” Elewski noted. "For Candida, I would give fluconazole 200 mg a day for a week.” If one suspected both Pseudomonas and Candida, a follow-up course of oral or topical Cipro, is logical. “I use Cipro otic drops and when I order it, I’m careful to remind patients, ‘do not put this in your ear; I am treating your toe. Put it on your toe.’” Alternatively, a vinegar soak works well against Pseudomonas, but Elewski recommends adding gentamycin ointment.

Hydroquinone exposure is another cause of black-nail anxiety Elewski has encountered. The photo she shared was of long nails that appeared “blackish. ”As a dermatologic detective, you need to be thorough with a history to ferret out potential causes. The patient was applying bleaching cream containing hydroquinone. In the sun, hydroquinone oxidizes to quinone which then polymerizes to a dark brown to blackish color, Elewski said. She used to encounter the discoloration more often when hydroquinone was still available over the counter, but she still sees patients who are prescribed the topical alarmed by the change in nail color. “So how do you know for sure that's what it is? You can reassure the patient by getting a 15 blade and scraping off the pigment.” The black nail is now cured, and the patient is educated on how to avoid a recurrence.

While benign causes are frequent, clinicians must remain vigilant for melanonychia and follow the ABCDEFs longitudinal pigmented lines. "Be particularly careful about the width of the band," the “B” in the mnemonic, Elewski cautioned. “Measure the band; document the width in your notes; document that it is straight, note the color, and take a photo.” If you are concerned, a biopsy is indicated.

Elewski made clear that while she had included light comments in her case presentations, the sudden appearance of a darkly pigmented nail for a patient feels like an emergency, and the patient's alarm should be acknowledged, respected, and allayed pending a thorough investigation.