A melanoma may cause a small amount of pain if it appears under the toenail. However, it may also have no symptoms at all. Melanomas under the toenail often appear as brown or black streaks, according to WebMD.
Pain is not one of the typical symptoms looked for when diagnosing melanomas. These skin cancers typically appear as growths on the skin notable for their asymmetrical shape, border irregularity and color irregularity, as WebMD explains. They are typically at least the size of a pencil eraser, and they often change in size or shape. They may cause some bleeding or itchiness. Melanomas may also grow within an existing mole; in this case, the size, shape, color or consistency of the mole may change.