Dear Science,
When I take a shower with cold feet, it feels like the hot water
is burning them. Is it? Is this bad for my feet?
Cold Feet
So long as the water doesn’t feel too hot elsewhere on your body,
your feet are safe—although Science suspects you need a bath mat,
pronto.
Why does it hurt? Because the neural circuitry connecting your
body to your brain is indistinguishable from that box of Christmas
lights you never bothered to untangle before plugging in. Signals from
your hot and cold sensors travel on the same neural circuitry—the
ventral spinal cord pathways—as from your pain sensors. Smart
work there, intelligent designer.
The human body has both cold and hot sensors—neither works
like a thermometer you’d use to take your temperature. Your sensors
tend to be more focused on detecting rapid changes—down or up, respectively—in
temperature. You know how this works. When you jump into a warm shower,
it feels shockingly hot. After a minute or so, even though the water is
packing the same heat, it just feels warm. The sensors have adapted to
the new temperature, with the hot and cold sensors settling down to the
new normal. Hop out of the shower—another quick change—and
the cold sensors go crazy. Brrr.
Just before the shower, your feet are probably on a really cold
floor. When the hot water hits, the rapid change in temperature
causes the heat sensors in your feet to freak out and signal like
mad—so much so that the signal is probably spilling over to
the part of the circuitry in your spinal cord normally used for the
pain sensors. So, when the signal makes it up to your brain, it’s
hot and ouch when it should just be ahh. For a
similar reason, this is why cold showers hurt—with the cold
sensors signaling so strongly, thanks to the quick change downward in
temperature, that the firing spills over to the pain-sensor side of the
track.
How do we know all this? Lots of earnest and patient dissection by
Hensel and Kenshalo in 1969 isolated the warm and cold receptors. The
receptors were pinned and hooked up to amplifiers so the weak
electrical signals generated by each could be read. Anything from 30O C
to 45O C (where heat stops and barbecue begins) caused the warm
sensors to fire off electrical impulses, with sudden shifts upward
causing a cacophony of electrical pulses.
Science loves the hot shower in the morning more than anything
else—craving the jolt to the temperature and pain systems
caused by that first burst of hot water on the body. Civilization is
worth saving for that alone.
Sensitively Yours,
Science
Send your science questions to
dearscience@thestranger.com.
jus like my fist bong hit in the mourning… love that felling
If memory serves correctly, the body actually has sensors that react to cold and warm with hot being detected by simultaneous activation of both. This can be verified by an old experiment that involves two metal pipes spiraled together, one with cold water the other warm. Touch each pipe independently and you can sense cold or warm as appropriate. Wrap your hand around both and how long it takes for you to pull your hand away. It burns, even though there is not sufficient heat to injure you.