Poor “Touch” Response
Question: Why doesn’t my cell phone respond to my polio hand when my fingers are cold?
Dr. Bruno’s Response: STOP Post-Polio "Zombie Finger!” Cell phone screens - actually almost all screens that respond to touch – sit above scores of small, individual electric fields created beneath each “button”. When your finger touches the screen (or even hovers above the surface) the skin’s capacitance (its ability to hold an electric charge) disturbs the electric fields and activates the buttons. The skin’s capacitance is not dependent on the temperature of your skin but on how much electrically-conductive liquid (moisture, blood) is in the tip of your finger. (You'll notice that your fingernail will not activate a touchscreen button because it's made of keratin, a dry, hardened protein.)
As polio survivors know all too well, low temperatures cause significant cooling of the skin by decreasing the amount of blood in your fingers and can thereby decrease capacitance of finger tips. Low humidity dries out your skin and will also decrease skin capacitance. Without even measuring blood flow, skin temperature or humidity, one study found that skin capacitance decreased by 21% between summer and winter. (Lubriderm anyone?) If your fingertip blood flow drops and your skin becomes dry, polio survivors can develop low capacitance “Zombie Finger,” where all the button pushing in the world will not make your phone respond. So, when the cold weather comes, wear gloves and moisturize. The “Zombie Finger” you prevent will be your own.