Science Q&A

Do nails thicken at different speeds?

New York TimesOctober 28, 2012 

Q: Why do toenails thicken as we age, but fingernails don’t?

With age, there is a rapid decrease in the growth rate for both toenails and fingernails, said Dr. Richard Scher, head of the nail section at Weill Cornell Medical College. As a result, both kinds of nail thicken, because of the piling up of nail cells, called onychocytes. Fingernails do not thicken as much, however, because the decrease in their rate of growth is much smaller. And fingernails tend to be filed and buffed much more, which thins them.

Other factors that can affect the rate of thickening include long-term trauma and impaired circulation.

Feet, more than hands, are under constant stress, said Dr. Tzvi Bar-David, director of the podiatric surgery service at New York-Presbyterian/Columbia hospital.

“We walk many miles daily, and most often in a closed shoe,” he said.

Trauma from falling objects, stubbing injuries, athletic wear and tear, and poorly fitting shoes can alter the cells from which the nails grow, Bar-David said, and repetitive incidents or one severe episode can thicken or disfigure the nail plate.

Q: Does your heart really skip a beat when you sneeze?

Sneezing can slow your heart rate, but the effect is minimal.

Just before sneezing, most people take a deep breath. This increases pressure in the chest and briefly inhibits the flow of blood to the heart, which can lower blood pressure and increase the heart rate. But as you exhale, your blood pressure increases and heart rate, in turn, goes down. At the same time, sneezing stimulates the vagus nerve, which runs from the brain through the abdomen. In general, any time the vagus nerve is stimulated, the body’s response is to reduce the heart rate. The effect of this is minimal, however, slowing the heart perhaps only a single beat.

This phenomenon is not unique to sneezing, said Dr. Christopher Magovern, a cardiothoracic surgeon at Morristown Medical Center in New Jersey. Coughing, gagging and other acts can have a similar effect on the vagus nerve.

“There’s nothing special about the sneeze,” he said. “Your heart can slow down, skip a beat, or stop momentarily. But it resumes.”

For most people this goes unnoticed. But in extremely rare cases, sneezing can slow the heart rate or lower blood pressure to such an extent that it causes a person to pass out.

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