Nail trauma: A Thumb-nail Sketch
Your fingernails and toenails are there to help prevent injury to your digits, so from time to time your nails are likely to get injured in the line of duty (or in the strike line of a hammer's head). Nail injuries can cause bruising, infection and may sometimes stunt nail growth.
Keeping your nails short can help prevent nail injury because you'll be less likely to snag a nail or separate it from the nail bed. And while you can't always prevent an accidental injury such as shutting your finger in a door or drawer, you can help reduce the risk of nail bed trauma with a little common sense: Don't use your fingernails as if they were tools.