If your nails have taken on a yellow tint (like mine sometimes do), it may be your lungs crying out for help...or just evidence of polish color preference. "While yellow nails can be a sign of lung disease or nicotine stains from smoking, more often, it's discoloration from using dark nail polishes," Steel says. Phew. But if you notice an unpleasant odor, you could have a fungal infection. Make an appointment with your doctor asap — a simple blood test can rule out illnesses that cause yellowing. If it's just a matter of your polish staining your nails, switch to one of these lighter polish colors. And if you must use dark polishes, always use a base coat, like this OPI one, to protect your nail from direct contact with the pigment.

When it comes to early skin cancer detection, we've been warned to take a second look at moles and freckles, and now it's time to add fingernails to that checklist. "All individuals should be aware of skin cancer — particularly melanoma and squamous cell cancer — which can occur on, in, or around the nails," says Steele. "A new or expanding dark streak in the nail, or a dark bump or sore may be a sign of skin cancer and should be evaluated." The good news for my fellow polish addicts: Sunlight is unable to penetrate through polish, so count that as your nail sunscreen...just be sure to take a breather and really examine both your nails and your cuticles for dark areas. Like to wear the bare look? Be sure to cover all of your fingers when applying sunscreen, or pick up Orly Sunscreen for Nails, a clear top coat that keeps UV rays at bay.

If your natural nails have turned two-toned (a condition called Lindsay's nails, after the doctor who first described the half-and-half nail back in 1967), get your kidneys checked out, says Steele. When the kidneys are damaged or begin to fail, waste products and fluid build up, causing swelling throughout body — even in the nail beds. This causes the small half-moon portion of the nail just above the cuticle, called the Lunula (Latin for "little moon"), to rise and extend halfway up the nail, creating the half and half pattern.

Nudes and neutrals may be in, but if your nails are looking more ghostly than usual, a variety of conditions could be causing it, including anemia, diabetes or liver disease. According to Steele, pale nails get classified under the medical term leukonychia, but it is a non-specific finding that can mean a number of things, even a bad reaction to medication or a fungal infection. The only way to find out is a check-up — schedule an appointment with your doctor if you notice a change.

If your natural nails are blue-ish, they're telling you they can't breathe. Your body may be having a hard time delivering enough oxygen where it needs to go. According to Steele, blue discoloration of the fingertips is associated with poor oxygenation and vasospasm, a condition where the blood vessels constrict and decrease blood flow in the body. In some cases, this is associated with autoimmune diseases, or with Porphyria, a rare disorder that some individuals are born with. However, some people naturally have slower or poor blood circulation (especially those who live in colder climates). If your nails are persistently blue, have a physician check your blood and oxygenation levels to see if something more serious is up.