What can cause brown discoloration of my nails?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Brown discoloration of the nails, medically known as melanonychia, occurs when pigment-producing cells (melanocytes) deposit melanin in the nail. Common causes include:

Benign factors: trauma, aging, pregnancy, or ethnic pigmentation variations
Medical conditions: fungal infections, psoriasis, or endocrine disorders
Medications: chemotherapy drugs, antimalarials, or certain antibiotics
Serious concerns: subungual melanoma, a rare but dangerous skin cancer

While many cases are harmless, a single dark stripe, sudden changes, or pigmentation spreading to surrounding skin warrant prompt medical evaluation.

Because brown nail discoloration can range from completely harmless to a warning sign of something serious, understanding your specific symptoms is the critical first step. Rather than guessing—or worrying unnecessarily—take a free, instant, online symptom check to receive personalized insights about possible causes and clear guidance on your next steps. It takes just a few minutes and could help you decide whether home monitoring is enough or whether you should see a specialist right away.

Reviewed for medical accuracy: 07/15/2026

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Explanation

Brown discoloration of the nails, also known as melanonychia, can occur for several reasons. It may be harmless, like a mole under the nail, or more serious, such as a sign of melanoma, a type of skin cancer. Sometimes, melanonychia appears as a brown or black stripe along the nail, which is called longitudinal melanonychia.

Possible Causes:

Benign Causes:

Pigmented moles or freckles
Trauma or injury to the nail
Fungal infections

Serious Causes:

Melanoma, a type of skin cancer

Melanonychia can be a clue to a correct diagnosis, so it is essential to pay attention to any changes in your nails. If you notice new or changing brown discoloration, you can start by using our free AI symptom checker to better understand your symptoms and determine whether the condition is benign or if further investigation is needed.

Understanding the appearance and changes in your nails can help in recognizing whether the condition is benign or requires medical attention. Always seek professional advice if you are unsure about changes in your nails.

(References)

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.
Johannessen JT, & Juel J. (2023). Benign or malign disturbances of the nail apparatus. Ugeskrift for laeger, 38018740.

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