Melanonychia: Black or Brown Lines in Your Nail
Melanonychia may appear in one nail or several. These lines can occur naturally if you have a dark complexion.
No matter the cause, have a doctor check for melanonychia because the lines may be a sign of other health issues. Melanonychia is also called melanonychia striata or longitudinal melanonychia.
There are two broad types of melanonychia:
- Melanocytic activation: This is an increase in the production and deposits of melanin in your nail but not an increase in pigment cells. Causes include trauma, nutritional deficiency, and medication.
- Melanocytic hyperplasia: This is an increase in pigment cells in your nail bed. This growth can be benign or malignant.
Melanonychia can appear in fingernails or toenails. It can also occur in more than one nail.
It may look like:
- a black or brown vertical stripe down the length of the nail
- a black or brown discoloration stripe spread across the nail
- a structural irregularity of the nail
The nails of your toes or fingers are usually translucent and nonpigmented. Melanonychia occurs when the pigment cells, called melanocytes, deposit melanin — brown-colored pigment — into the nail. These deposits are usually grouped together. As your nail grows, a stripe of brown or black appears.
Melanin deposits are caused by two primary processes, which have different causes.
Causes of melanocytic activation can include:
