Is black discoloration of the nails related to cancer?

Nail discoloration to black may be associated with cancer, but not all cases of black nails are caused by cancer. Some types of skin cancer can present as dark streaks or patches under the nail; however, in most cases, black nails are due to benign causes such as trauma or fungal infections, which require professional evaluation for accurate differentiation. If any discomfort occurs, prompt medical consultation is recommended.

When nail darkening is caused by cancer, it often appears as a black patch or vertical dark line under the nail with irregular borders and uneven pigmentation. It may be accompanied by nail damage, nail plate thickening, and in some patients, swelling or pain in the fingertips or toes. A definitive diagnosis requires pathological examination, and early intervention and treatment are essential.

In most instances, black nails result from benign factors—such as bruising due to pressure or impact on the nail, or onychomycosis (fungal nail infection). Bruising typically resolves gradually over time, while fungal infections require antifungal medication. With proper treatment, nail color usually returns to normal, so there is generally no need for excessive concern.

In daily life, it's important to protect nails from injury, keep them clean and dry to prevent fungal infections, avoid scraping or irritating the nail when discoloration appears, monitor changes regularly, complete medical evaluations as advised, and seek timely follow-up if abnormalities occur, to prevent delays in diagnosis and treatment.