What might cause my nails to become discolored and black?

Q: What might cause my nails to become discolored and black?

Black discoloration of the nails is often caused by **melanonychia**, a condition marked by dark brown or black streaks running along the nail. Common causes include nail trauma or injury, fungal infections, certain medications, vitamin deficiencies, and underlying medical conditions such as endocrine disorders or, in rare cases, melanoma. While many causes are harmless, persistent or spreading dark streaks should never be ignored, as early evaluation can be critical. Because black nail discoloration can range from a minor bruise to a sign of something more serious, understanding the likely cause is an important first step. A free, instant, online symptom check can help you quickly identify possible conditions linked to your symptoms and guide you on what to do next—saving you time, easing worry, and helping you decide whether self-care or a doctor's visit is needed. Reviewed for medical accuracy: 07/15/2026

Reviewed by Yoshinori Abe, MD

Internal Medicine

Black discoloration of the nails is often caused by melanonychia, a condition marked by dark brown or black streaks running along the nail. Common causes include nail trauma or injury, fungal infections, certain medications, vitamin deficiencies, and underlying medical conditions such as endocrine disorders or, in rare cases, melanoma. While many causes are harmless, persistent or spreading dark streaks should never be ignored, as early evaluation can be critical.

Because black nail discoloration can range from a minor bruise to a sign of something more serious, understanding the likely cause is an important first step. A free, instant, online symptom check can help you quickly identify possible conditions linked to your symptoms and guide you on what to do next—saving you time, easing worry, and helping you decide whether self-care or a doctor's visit is needed.

Reviewed for medical accuracy: 07/15/2026

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Explanation

Melanonychia is a condition where the nails develop dark streaks or become discolored. This can happen for several reasons:

Injury: Sometimes, an injury to the nail can cause bleeding under the nail, leading to a black appearance.
Medical Conditions: Some health issues, like fungal infections or certain skin conditions, can also cause nails to change color.
Medications: Certain medications might affect nail color as a side effect.
Melanonychia: This is a specific condition where there is increased pigment in the nail, often appearing as a dark streak. It can be due to benign causes or more serious concerns like melanoma.

If you notice changes in your nail color, especially if it's a new change, you can use a free symptom checker to help identify potential causes and determine whether you should consult a healthcare professional for appropriate advice.

(References)

Singal A, & Bisherwal K. (2020). Melanonychia: Etiology, Diagnosis, and Treatment. Indian dermatology online journal, 32055501.
Haneke E, & Baran R. (2001). Longitudinal melanonychia. Dermatologic surgery : official publication for American Society for Dermatologic Surgery [et al.], 11442597.
Gradinaru TC, Mihai M, Beiu C, Tebeica T, & Giurcaneanu C. (2020). Melanonychia - Clues for a Correct Diagnosis. Cureus, 32064201.

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