Look for: Uniformly widened fingertips or toes -- they appear to bulge out beyond the last knuckle -- where the nails have widened, too, so that they curve down and appear to wrap around the tips of the finger like an upside-down spoon. (Normal nails are narrower than their base fingers.) These extra-wide nails are called "clubbed" nails.
What it might mean: Clubbed nails are a common sign of pulmonary (lung) disease, Newburger says. Although the nails' odd shape develops over many months to years, people are often unaware of the underlying condition, which can include lung cancer.
Next steps: If you haven't had a physical exam lately, consider one, especially if you have other symptoms such as coughing or shortness of breath.
Look for: Nail beds that have little dips in them, an effect called koilonychia, or "spooning." "If you put your hand flat on the table, the spooned nails look like they could each hold liquid," Newburger says. The nails will also be unusually pale or stay whitish for more than a minute after you press gently on one. (Normally it would turn white for a second or two before returning to its original pinkish color.) The moons at the base of the nails may look particularly white.
What it might mean: Iron-deficiency anemia. Spooning can also be seen in the nails of people with hemochromatosis, or "iron overload disease," a condition usually caused by a defective gene that leads to too much iron being absorbed from the gastrointestinal tract. Other symptoms for both conditions can include fatigue and lack of energy, or they may be symptomless.
Next steps: A complete blood count can diagnose anemia, and a physical exam might pinpoint the cause of iron problems. Iron supplements and dietary changes are often prescribed as first-line treatments for anemia.