What Your Nails Reveal About Your Health

3.Dark Lines Beneath the Nail

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Dark lines under nails can come from injury, like pinching a finger. But if dark streaks appear without trauma, see a doctor right away, as it could signal skin cancer. Called melanonychia, these streaks are most concerning if only one nail is affected. Some lines are harmless, related to medicine, pregnancy, or ethnicity, but any new or changing line should be checked. Subungual melanoma is the most serious risk. Early detection is vital, so have any unexplained dark line—especially one that gets wider or darker—examined quickly.