Brittle, cracked nails can ruin a good manicure, but there are bigger issues at stake here — namely, your thyroid gland. Your thyroid gland produces hormones and plays a major role in regulating your metabolism and energy. If it's underactive and hormone levels are low, it usually manifests as dry skin, hair that falls out, and very brittle nails that struggle to grow. If this is the case, ask your doctor for a quick blood test to find out if your hormone levels and thyroid are normal. On a less scary but still depressing note, brittle nails are also a classic sign of getting old, says Steele. "This is especially true of ridging and brittleness. The intrinsic moisture in the nail tends to decline with age, as it does the moisture in our skin."

If you have linear ridges, known in the medical world as Beau's Lines, your nails are trying to tell you something. You may be vitamin or mineral deficient (lack of zinc can cause the ridges), it could be a bad allergic reaction to a new polish, or something more serious, like diabetes. "Beau's Lines can be associated with anything that stresses the body and requires it to divert resources away from nail growth," says Steele. "This could be anything from a surgery, to severe illness, or a reaction to certain medications." Don't rush to WebMD to diagnose yourself; make an appointment with your doctor to find out of this is a minor reaction or a major health concern.

If your nail folds are red, swollen, and tender, chances are you have an infection, According to Steele, puffy nail folds tend to occur with a condition called paronychia, but don't let the big name scare you. Paronychia is a skin infection that occurs around the nails and is fairly common. It can be caused by a bacterial or fungal infection from everyday trauma and inflammation — think: nervously gnawing your cuticles, picking a hangnail, or simply over-washing your hands.

Clubbed nails are hard to miss, and they are not to be taken lightly — this nail condition can signal a serious illness, says Steele. "Clubbing of the nails is typically a sign of long-standing or severe cardiovascular or lung disease and poor oxygenation," says Steele. And the list only goes on — clubbed nails can also signal cyanotic congenital heart disease, cystic fibrosis, and chronic inflammatory bowel disease. All of these diseases cause the small arteries in the fingertips to dilate, which enlarges the tissues of the nail beds and causes the fingernails to club.

If your nails are more concave than clubbed, you may have a condition called koilonychias, or spoon nails. "Spoon nails can be associated with iron deficiency to the point of anemia, but it is usually a rare association," says Steele. "Most people with spoon nails do not have an underlying cause, but it is worth getting evaluated to make sure iron and blood counts are normal."