Picture of Clubbed Nails
Clubbed nails occur when your fingertips bulge and the nails curve down and get shiny. The condition is usually one you are born with, but you may have other health issues as well such as heart disease or lung disease. It's unclear what causes clubbed nails, but it happens when there are certain substances in your blood such as vascular endothelial growth factor (VEGF). Your body produces more VEGF when it can't get enough oxygen.
Text Source: Medline Plus / National Library of Medicine