A black line or streak that appears in a nail is often from some type of injury. But if you don't remember accidentally whacking your index finger or stubbing your toe on a table leg, start looking elsewhere for an explanation. These black lines could be warning signs of melanoma, an extremely dangerous type of skin cancer, so you should see a doctor to have them checked out. when see change in nail you need note and checking. Keep good nail will help you health. if you have any money i think need go to nail salon to care your nail.