By Anthony L. Komaroff, M.D.

DEAR DOCTOR K:

I've always been proud of my smooth, healthy-looking fingernails, but recently I've noticed some changes. I have developed vertical ridges in my nails and, although I'm not sure if I'm imagining it, they also seem thicker. Should I be alarmed by these changes?

DEAR READER:

It's true that healthy people usually have normal-appearing nails. The trouble is, so do most sick people. Normal nails are smooth, uniformly shaped and uniformly colored, often with a lighter, half-moon shape under the nail near the cuticle.

But even healthy people can have nails that aren't fit for a photo shoot. Vertical ridges like the type you've developed are found in perfectly healthy people. So are occasional "pits" (indentations), darkened bands, and flatter or rounded nails.

That said, your nails can sometimes reflect past illnesses. Sometimes you can tell if someone was sick several months ago by the appearance of a horizontal ridge or indentation in the nail, called Beau's lines. These lines may occur after any serious illness, including those associated with a high fever or severe nutritional deficiency. They may also appear soon after getting chemotherapy for cancer.

There also are some nail changes that may indicate an underlying illness, one you may not know about. If your nail changes match up with any of the following, I would consider it a red flag and recommend that you visit your doctor and discuss your symptoms. Here are a few conditions that can affect your nails:

-- Lung disease. Conditions such as lung cancer, extensive lung scarring and cystic fibrosis can be associated with clubbing of the nails. Try this: Stick out your index finger and turn it sideways in front of your face, so that you're looking at it from the side. Look at where the nail first comes out from under the skin until it ends. Is it flat, or is it rounded up in the middle, rising and then falling till the nail ends? If it's rounded up, that could be clubbing. It doesn't always indicate an underlying medical problem, but it's worth pursuing with your doctor.

-- Psoriasis. Small indentations (called pits) and thickening of the nails are common in people who have psoriasis. On the other hand, if you have psoriasis, you will already know it from its effects on your skin.

-- Heart valve infection (endocarditis). A heart valve infection is a serious condition and can be hard to diagnose. The appearance of painless red lines running vertically under the nails may indicate endocarditis. Called splinter hermorrhages, they look like splinters that got caught under the nail, except they don't hurt.

If your toenails become thickened, discolored or brittle, it may mean you have a toenail fungus infection. You don't need to have it treated unless it is painful or just looks ugly. If you have diabetes, and therefore are vulnerable to skin infections and foot sores, it's wise to get it treated.

Though your nails can say a lot about your health, the reality is that doctors usually have better ways to tell if you're healthy or not.

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Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.

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