Dermatology Questions? Ask an Online Dermatologist.
Can you attach the photos here? Pain or itch? Any other symptoms? Any medical problems? Any surgeries? Any medications? Any family medical history?
It seems to be longitudinal melanonychia which is a banded brown to black pigmentation of the nail due to the presence of melanin in the nail plate. It may result from activation or hyperplasia of nail matrix melanocytes. There are many possible causes such as physiologic (ethnic or pregnancy-related), traumatic, dermatologic, systemic, or iatrogenic factors. Vitamin B12 deficiency, vitamin D deficiency causes it. You should see your doctor to refer a dermatologist to have exam and tests.