There are several possibilities to consider in this case of a black spot on the toenail cap. In most cases, it may be a localized trauma that has caused stasis of blood under the nail. If the stasis of blood under the nail occurs after a certain period of time, the clot may gradually form a darker black spot, which is a blood clot. So, in this case, it may gradually fade away. However, there is also a possibility that the black spots may be formed by some pigmented nevi under the toenail, but these black spots may generally be uniform and gradually form a strip-like manifestation and are progressive. However, there is another possibility, which is malignant melanoma. If this is the case, it usually shows a darker local color or an uneven black color, which requires a dermatoscopic examination to be able to determine. Some may even require dermatopathology to determine if it is a malignant melanoma.