Looking at your photo, this is a pale/whitish longitudinal nail ridge â not a dark stripe. Melanoma (subungual) presents as a dark brown or black band, often with pigment spreading to the skin around the nail (Hutchinson's sign). What you have looks like benign longitudinal ridging (onychorrhexis), which is very common, especially with age or minor repetitive trauma to the nail matrix. Not something to worry about based on the photo.
Next Steps
No urgent action needed. However, if the line turns dark (brown/black) or pigment spreads to the skin around the nail, see a dermatologist promptly for evaluation.