10 Nail Changes That May Indicate an Underlying Health Issue

7. Melanonychia - Dark Streaks and Cancer Concerns

Melanonychia refers to brown or black pigmentation of the nail, which can appear as diffuse discoloration or as distinct longitudinal bands running from the cuticle to the free edge of the nail. This pigmentation results from increased melanin production by melanocytes in the nail matrix or nail bed, and while it can be benign, it may also indicate serious conditions including melanoma. Longitudinal melanonychia, presenting as dark vertical bands, is more common in individuals with darker skin tones and can be a normal variant, particularly when it affects multiple nails symmetrically. However, new-onset melanonychia in fair-skinned individuals, or changes in existing pigmented bands, require careful evaluation to rule out subungual melanoma, a potentially deadly form of skin cancer that accounts for 1-3% of all melanomas. Warning signs include irregular borders, color variation within the band, width greater than 3 millimeters, extension of pigmentation onto the surrounding skin (Hutchinson's sign), and involvement of a single digit, particularly the thumb or great toe. Benign causes of melanonychia include trauma, certain medications (such as antimalarials, chemotherapy agents, and antimicrobials), endocrine disorders, nutritional deficiencies, and inflammatory conditions. Ethnic melanonychia, common in individuals of African, Asian, or Hispanic descent, typically presents as multiple uniform bands that remain stable over time. Any new or changing melanonychia, especially in light-skinned individuals or when accompanied by nail dystrophy, pain, or bleeding, requires prompt dermatological evaluation and possible biopsy to exclude malignancy.