What Your Fingernails Say About Your Hidden Health Issues

3.Dark Lines Beneath the Nail

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Dark lines or marks under the nails can result from trauma, such as pinching your finger in a door, dropping heavy objects on your foot, or other injuries that cause bleeding beneath the nail plate. However, if you notice dark streaks appearing without any recent injury or trauma, it is critically important to see a doctor immediately, as this can be a sign of skin cancer, specifically a dangerous form called subungual melanoma that develops under the nail. Medically known as melanonychia, these dark streaks are especially concerning if they appear on a single nail, change in width or color over time, or extend into the surrounding skin tissue. While some lines can be harmless and related to certain medications, pregnancy hormones, genetic factors, or ethnicity, any new or changing line should be checked by a qualified healthcare provider or dermatologist without delay.

Subungual melanoma, a type of skin cancer that occurs beneath the nail, is the most serious concern and requires immediate medical attention for proper diagnosis and treatment. Early detection is absolutely crucial for successful treatment outcomes, so any unexplained dark line—especially one that gets wider, darker, or changes in appearance—should be evaluated promptly by a medical professional who can perform appropriate tests and determine the best course of action.