A nevus of the nail does not usually cause pain. A nevus of the nail, also known as a nevus of the nail matrix, is a pigmented nevus of the nail matrix (histologically usually called a junctional nevus), which manifests itself as a longitudinal brown to black streak of melanin that spills over into the nail plate and pushes forward to the edge of the nail as the nail plate grows. It usually presents as a black line on the nail with no other manifestations. Nail moles do not usually cause pain. If the nail is painful, it may be caused by trauma, onychomycosis, cancerous onychomycosis, etc. Pay attention to the differentiation of pain sites. If the black line of the nail widens rapidly for a short period of time and is accompanied by pain, weight loss or other clinical manifestations, melanoma may be suspected. If the nevus is cancerous, it may be accompanied by pain, but it is rare in clinical practice. If the above symptoms occur, please go to a regular hospital for tissue biopsy to determine the cause of the disease.