Vertical lines and black lines on the thumbnail are mostly symptoms of nail dystrophy, onychomycosis, or onychomycotic nevus, which can be treated with nail protection, supplementation, antifungal, or surgery. 1. Protect your nails: avoid contact with chemicals with strong acidity and alkalinity, and wear rubber gloves if you need to work. Don’t dye your nails or put on nail patches to avoid nail injuries. 2. Supplementary nutrition: Nails with vertical lines and black lines are related to the lack of calcium and zinc, you can eat more calcium and zinc-rich foods such as milk, oysters, meat and so on. You can eat more food rich in calcium and zinc, such as milk, oysters, meat, etc. Or take multivitamin tablets or calcium, iron and zinc chewable tablets for treatment. 3. Hand lines and black lines caused by ringworm can be treated with antifungal therapy, such as topical amorolfine application, compound povidone-iodine application, or oral itraconazole capsules, fluconazole tablets and other antifungal drugs. 4. Surgical treatment can be considered for onychomatous nevus, after removing the corresponding nail, the pigmented nevus at the onychomatous nevus can be removed, and then wait for the nail to grow back again. Nails with vertical black lines are also seen in other causes, it is recommended to consult a doctor in a timely manner, under the guidance of a professional doctor to standardize the treatment, so as not to delay the condition.