So while rubbing your skin won't undo any damage of a bonked head, to a certain degree it will close off pain information to the brain and make you feel better.
"Anything you did to increase input into these pressure nerve fibers would allow input of endorphins in the spinal cord," says Warfield.
And "anything" may even include electric catfish.
It turns out that millennia before a Canadian and British physician explained Gate Theory, the ancient Egyptians stumbled upon an application of it.
"Ancient Egyptians used to pull these electric catfish out of the Nile and put them on the painful area," says Warfield.
Just as rubbing a stubbed toe shuts a gate within the spinal cord, so can electric stimulation fire up the pressure nerves.
Healthcare providers today use electrical signals in a less fishy, decidedly less sloppy application called a TENS device — short for transcutaneous electrical nerve stimulation.
"The disadvantage of the conventional mode TENS is that it is temporary," says Brian Murray, a physical therapist and rehab team coordinator at Johns Hopkins University in Baltimore, Md. "People can build a tolerance."
However, stimulating the skin with a TENS unit can help many different types of pain — a weekend warrior who's injured himself, a person recovering from surgery, or a person in chronic pain who's trying to function — all relatively easily.
"It's not something where we strap them down to the table and wait until their hair stands up," says Murray. "You end up with a tingling feeling as if your foot falls asleep."