Hold that polish! Or at least give your nails a good look before you paint them. Your fingernails and toenails are like 20 mini-mirrors to the state of your overall health. Changes throughout the body that are otherwise invisible can sometimes be first seen in the nails, says dermatologist Amy Newburger, a senior attending physician at St. Luke's - Roosevelt Medical Consortium in New York City.
Fingernails tend to give more reliable clues than toenails, given the wear and tear of walking, tight shoes, and slower foot circulation over time, which can obscure toenail changes. But check both hands and feet -- the first of the following nine nail clues explains why.
Clue 1: A black line
Look for: A black discoloration that's a straight vertical line or streak and grows from the nail bed, usually on a single nail. About 75 percent of cases involve the big toe or the thumb, according to a review in the British Journal of Dermatology. Especially worrisome: a discoloration that's increasing or that's wider at the lower part of the nail than the tip. "That tells you that whatever is producing the pigment is producing more of it," says Newburger.
Also beware when the skin below the nail is deeply pigmented as well, says podiatrist Jane Andersen of Chapel Hill, North Carolina, a spokeswoman for the American Podiatric Medical Association.
What it might mean: Melanoma, the deadliest form of cancer. People with darker skin are more vulnerable than Caucasians to subungual melanoma (melanoma of the nail bed), but darker-skinned races also have more dark lines in nails that are benign, according to a 2004 report in American Family Physician.
Next steps: Always have a doctor check out a suspicious black line on the nail quickly because of the high skin cancer risk. A black line on the nail may also be caused by a harmless mole or an injury. A biopsy can confirm melanoma.
Clue 2: Small vertical red lines
Look for: Red (or sometimes brownish red) streaks in the nail. "They look like blood or dried blood," Anderson says. These are known as "splinter hemorrhages" because they look like a splinter but are caused by bleeding (hemorrhage) under the fingernail or toenail. They run in the same direction as nail growth.
What it might mean: Heart trouble. The "splinters" are caused by tiny clots that damage the small capillaries beneath the nail. They're associated with an infection of the heart valves known as endocarditis. Don't panic if you see one, though: Sometimes an ordinary injury to the nail can cause a splinter hemorrhage.
Next steps: No treatment is needed for the splinter hemorrhage itself. A doctor can evaluate and treat the underlying cause if it's heart-related.
Clue 3: Wide, "clubbed" nails
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.
Clue 4: Spoon-like depressions
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.
More things your nails say about your health
Clue 5: Rippled, pitted nails
Look for: Tiny indentations or holes in the nail bed called "pits." The nail may also appear to be rippled rather than smooth. (You can also feel these abnormalities by rubbing your finger across the nail, which is normally as smooth as the inside of a seashell.)
What it might mean: Psoriasis. Between 10 and 50 percent of patients with this common skin disease have pitted, hole-pocked nails, according to a 2000 report in Primary Care. So do more than three-fourths of those with psoriatic arthritis, a related disorder that affects the joints as well as the skin. More rarely, Reiter's syndrome and other diseases of connective tissue show this symptom.
Next steps: A doctor can prescribe medications to treat the underlying conditions. The nail bed can often be restored in psoriasis when the treatment starts early.
Clue 6: Brittle nails
Look for: Peeling, splitting, or easily cracking nails. Sometimes vertical ridges mar the surface, too. These telltale wrecked nails are sometimes called "hypothyroidism nails."
What it might mean: Thyroid disease. Hypothyroidism, or underactive thyroid, occurs when the thyroid gland doesn't make enough thyroid hormone. (Typically a patient's hair is also thin and brittle.) Metabolic functions throughout the body are disrupted, including the delivery of moisture to the nails. Pale, dry skin and hair that may fall out are related signs. Hyperthyroid (overactive thyroid) diseases, such as Grave's disease, may also cause brittle nails.
Next steps: Skip the over-the-counter nail strengtheners for persistently brittle nails and get thyroid levels checked; if thyroid disease is the cause, it's important to treat the root problem.
Clue 7: Nails that seem to be "lifting off"
Look for: The nail itself separating from the nail bed, which is the layer of skin directly under the nail. This effect, known medically as onycholysis, often begins at the fourth or fifth fingernail. Toes can also be affected. It's also called "Plummer's nails" (after the physician Stanley Plummer, who described them in 1918) or "dirty nails," because debris can accumulate and be seen.
What it might mean: Thyroid disease. Hyperthyroidism, in which too much thyroid hormone is produced, can cause excessive nail growth and lead to this deformation. Plummer's nails tend to occur in younger patients rather than older ones.
Next steps: Other hyperthyroidism symptoms to be aware of include fatigue, difficulty concentrating, increased appetite, weight loss, sweating, hair loss, itching, and protruding eyes.
Clue 8: Depressions running across the nail horizontally
Look for: White ridges running across the width of the nail bed. These so-called "Beau's lines" (after the French physician who described them) can occur in all or just one nail; if in all nails, they're at about the same place on all of them. They're actual ridges in the nail plate itself.
What it might mean: Diabetes, psoriasis, Raynaud's disease -- or just a trauma to the nail. Beta-blockers and drugs used in chemotherapy can also produce Beau's lines. Some people develop them simply as a result of aging.
Next steps: Consider this effect just one piece of a puzzle. Nails grow about 1 mm every six to ten days, so doctors use this measurement to estimate when the problem might have begun.
Clue 9: White bands running across the nail horizontally
Look for: The white-colored bands, known as "Mees' lines," run transverse (parallel to the white tips of the nails). They may affect one nail or several, occurring at about the same spot on each nail. Because the problem is in the nail itself, the line moves forward as the nail ages -- allowing doctors to date the time the problem began.
What it might mean: Arsenic poisoning! Hair and tissue samples should be tested to verify. It's pretty rare these days, Anderson says, but worth knowing about.
Next steps: Make an appointment to see a doctor -- and avoid eating anything you don't prepare yourself!