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Harvard Commentaries
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Medical Myths Medical Myths
 

A Handful of Fingernail Myths


October 23, 2012

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center


People seem fascinated by the fact that fingernails and toenails continue to grow after death. I'm not sure why, especially since it's not true. Maybe it's the grotesque image of the nails happily lengthening as the rest of the body shrivels and decays. But, enough about my favorite horror flick. As it turns out, fingernails and toenails are a rich source of medical myth and misunderstanding.

"Facts" That Aren't

Here are the five most common misconceptions about fingernails that I could find. As is true with many medical myths and misconceptions, there is at least some element of truth to many of these.

 

    • Eating gelatin will encourage healthy, longer nails. Gelatin is made of processed collagen. Collagen is an important protein that provides strength and elasticity to skin, cartilage that lines joint surfaces, tendons, ligaments and many other parts of the body. Gelatin used to come from the bones and skin of cattle. The primary source now is pig skin. Fingernails and toenails, on the other hand (get it?), are made up of keratin. Although it's also a structural protein, it is unrelated to gelatin. Eating gelatin or soaking your nails in it will not affect your nails in any way. And it's not clear why anyone would expect it to do so!
    • Looking at your nails is a reliable way to assess health. This may be true, but only occasionally. The appearance of the fingernails (see below) can sometimes suggest common and serious illnesses. But significant health problems are common among people with normal-appearing nails. And healthy people often have nails that don't look quite right.
    • Fingernails continue to grow after death. Over the first few days or weeks following death the fingernails and toenails appear to be more prominent. But this isn't due to continued nail growth. It's because the fingertips retract away from the nails as the tissues dehydrate. In addition, nails decompose more slowly than other body tissues. So, the apparent nail growth is just an illusion. A similar phenomenon accounts for the apparent growth of hair after a person dies.
    • Toenail fungus should always be treated. Toenail fungal infections are common, affecting up to 5% of the population. But for most people, it's only a cosmetic problem. With a fungal infection, nails may be thickened, discolored or brittle. Their appearance may be a source of embarrassment, too. But there's rarely a serious medical consequence. As a result, treatment is optional. There are some important exceptions: Fungal infections in the nail can be painful and people with diabetes may develop a more serious bacterial infection or ulcer as a complication of toenail fungus.

 

    • Bite your nails often enough and they'll never grow back again. This sounds a bit like the "cross your eyes and they'll get stuck" myth. As intuitive as it may seem, it's also untrue. Nails grow outward toward the fingertip from the nail bed which lies under the cuticle. Since nail biting usually damages the nail that is farthest away from the nail bed, nail growth is unaffected. Once a person stops biting his or her nails, the nail typically grows out healthy and normal. A word of caution, however: Nail biting may increase the risk of skin infections near the nail (called paronychia).

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Nails As a Clue to Health

Healthy people usually have normal-appearing nails. Of course, the same is true for sick people. Normal nails are smooth, uniformly shaped and uniformly colored, often with a lighter "half moon" shape under the nail near the cuticle (called the lunula). But, there is significant variability in the appearance of nails even among healthy people — vertical ridges, occasional "pits" (indentations), darkened bands, flatter or rounded configurations are all observed in perfectly healthy people.

Even nail growth varies a lot among healthy individuals. It takes about six months for a nail to replace itself. Toenails take 12 to 18 months. Some people have faster growing nails than others. The rate of growth, too, varies over a lifetime: It is faster among children and pregnant women, slower after age 20 and during breastfeeding.

A person's nails can also change over time. Most people notice that their fingernails tend to become more brittle and thinner with age; toenails do just the opposite. Finally, some people are able to grow long and strong nails while others can't. It's just the way things are.

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Nails As a Clue to Disease

There are hundreds of pages in dermatology and medical textbooks devoted to conditions that may be "detected" (or at least suspected) by looking at the nails. Besides fungal infections (as mentioned above), here are a few of the most notable:

    • Lung disease – Conditions, such as lung cancer, extensive lung scarring (called pulmonary fibrosis) and cystic fibrosis can be associated with clubbing of the nails. The nails take on a raised, rounded appearance, like a club. It's occasionally seen in healthy people whose nails have had this appearance all their lives.
    • Psoriasis – Small indentations, called pits, and thickening of the nails are common in people who have psoriasis, and the nail may be the first sign of this skin condition. In addition, people with nail involvement have a higher chance of developing a type of arthritis associated with psoriasis called psoriatic arthritis.
    • Heart valve infection (endocarditis) – A heart valve infection is a serious condition, and can be hard to diagnose. The appearance of multiple red lines under the nails — called "splinter hemorrhages" — may be an indication of endocarditis.

 

    • Anemia – A pale appearance to the nail bed is common when a person is very anemic. Unfortunately, examiners tend to disagree about how pale a particular person's nail beds are, so this is not a particularly reliable way to detect anemia.

Just about any serious illness can affect the growth and appearance of the nails. 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. The closer to the cuticle the lines are, the more recently the illness occured — perhaps a month or so ago. A ridge that is closer to the fingertip suggests an illness that occured up to five or six months earlier.

Unfortunately, fingernails and toenails are not a reliable way to diagnose disease. In fact, most ill people don't have the "classic" findings in their nails described above. In addition, some people with these "classic" nail abnormalities, such as clubbing, are perfectly healthy! Although "reading one's nails" is interesting and can even be entertaining, we have much better ways to evaluate a person's health and pinpoint disease.

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Owners' Manual for Nails

It would be nice if the human body came with an owners' manual. Even better, there should be a warranty! As for fingernails, little maintenance is required. Here's how you can keep your nails healthy.

    • Trim your nails regularly with clippers or manicure scissors to keep them short and smoothly rounded at the tips.
    • Protect them from injury by wearing gloves, for example, if you are performing manual labor; don't bite them.
    • Apply moisturizer to your hands and nails after they're wet.
    • Consider using a nail hardener or clear polish to strengthen the nail.
    • Limit use of nail polish remover to twice a month to avoid excessive nail dryness, which can make them brittle.

 

    • If you get manicures, stick with reputable nail salons that sterilize instruments. Better yet, bring your own.

It's rare that a person's nails are brittle or otherwise unhealthy due to inadequate dietary protein or other missing nutrients (another medical myth!). Usually the culprit is nail dehydration that results from living in a dry climate or from frequent use of nail polish remover. Moisturizers can help, but don't rely on supplements, gelatin, or diet to keep your nails in good shape.

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The Bottom Line

Misconceptions about fingernails are common. So are remedies claiming to make your nails better that cost time and money. But, like it or not, there's relatively little you can do to change the overall health of your nails. If you're worried that the appearance of your nails might be an indication of a disease, talk to your doctor. But don't be surprised if he or she focuses on other parts of the body. The best clues about your health usually lie elsewhere.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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