How come we occasionally get white spots on our fingernails? asks Alex Latham, a student in Brookville.

White spots on fingernails, according to dermatologists, are one of the most common body blemishes, as familiar to most of us as pimples and scars. In any 100 people, more than 60 will probably have a spotty nail or two.

The spots are so common -- but can seem so mysterious -- that people have come up with creative names for them. "Fortune spots," predicting good luck. "Sweethearts," tallying the number of romantic suitors. And even "lies," the fingernail version of Pinocchio's growing nose.

Dermatologists say the white marks crop up because we ding our fingers so often. The culprit? Anything from a miscaught softball to a jabbing cuticle stick.

Our fingernails are made of a protein called keratin. The spots are thought to be a mix of keratin and air, places where new nail cells were incompletely formed. Once the spotty part of the nail is pushed up from the nail bed by new growth, the spots rise higher and higher.

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Some claim that white spots are due to mineral deficiencies, like a diet lacking enough calcium or zinc. But in a 2011 U.K. study, diet questionnaires showed that there seemed to be no connection with calcium or zinc intake. But there was a correlation with activities that "knock hands" frequently, like many sports.

Still, there's a lot researchers don't know about the spots, since not many studies have been done. In 1979, Harry L. Arnold Jr., then a dermatologist and professor at the University of Hawaii, noted that there were many nail-spot mysteries. If spots were always the result of injuries to the nail bed, he wondered, then why did some make their first appearance nowhere near the nail's lunula (half-moon)?

Arnold also found other oddities. After slamming his right index finger in a car door, he noted, one physician found a white spot above the lunula a month later. The doctor then noticed that his left middle finger had a spot in the same place. And on his right hand, the index and middle fingers sported identically placed spots.

Arnold called these "sympathetic" white spots, since they appeared in a parallel pattern on both hands. He found other cases of such seemingly mirror-image spots on uninjured fingers after an injury to one nail. Arnold suggested that other mechanisms might be at work: Nail spots might also be under the control of the body's nervous system. It remains for research to find out if he was right.