Some nail conditions are harmless, others are signs of a more serious health problem. For example, yellow or green discoloration in your nails may be the result of a respiratory problem like chronic bronchitis, or from swelling of your hands (lymphedema). If you've had a heart attack, or other severe illness that limits the blood flow through your body, you might see indentations that run across your nails, called Beau's lines. These lines appear when growth at the area under your cuticle is interrupted by lack of oxygen or blood flow to the area. If you notice that your nail problems are associated with other signs and symptoms of an illness, make an appointment with your doctor to get it checked out.