What's wrong with a black line under your fingernail?

There are many reasons for black lines on nails: First, nail-mother nevus, nail-mother nevus is a kind of pigmented nevus, the most common symptom of nail-mother nevus is nail-black line, nail-mother nevus may be cancerous melanoma, so it needs attention. Second, onychomycosis, onychomycosis is fungal infection, it can cause a part to show turbidity, thickening, free, nail black line and so on. Third, nail malnutrition, nail malnutrition can show a thin deck, brittle, tarnish and color changes, etc., mainly related to the lack of nutrients in the body, malabsorption and so on. Fourth, nail trauma, nail trauma can show purple or brown lines in the nail, mainly caused by bleeding under the nail.