An international team of researchers have found that human body has an entirely unique and separate sensory system aside from the nerves that give most of us the ability to touch and feel.
This sensory network is located throughout our blood vessels and sweat glands, and is for most people, largely imperceptible.
"It's almost like hearing the subtle sound of a single instrument in the midst of a symphony," said senior author Dr Frank Rice, a Neuroscience Professor at Albany Medical College (AMC), who is a leading authority on the nerve supply to the skin.
"It is only when we shift focus away from the nerve endings associated with normal skin sensation that we can appreciate the sensation hidden in the background," Rice added.
The researchers came across the hidden sensory system while studying two unique patients who were diagnosed with a previously unknown abnormality.
These patients had an extremely rare condition called congenital insensitivity to pain, meaning that they were born with very little ability to feel pain.
Other rare individuals with this condition have excessively dry skin, often mutilate themselves accidentally and usually have severe mental handicaps.
"Although they had a few accidents over their lifetimes, what made these two patients unique was that they led normal lives. Excessive sweating brought them to the clinic, where we discovered their severe lack of pain sensation," said lead author Dr David Bowsher, Honorary Senior Research Fellow at the University of Liverpool's Pain Research Institute.
"Curiously, our conventional tests with sensitive instruments revealed that all their skin sensation was severely impaired, including their response to different temperatures and mechanical contact.
"But, for all intents and purposes, they had adequate sensation for daily living and could tell what is warm and cold, what is touching them, and what is rough and smooth," he added.
Rice said under normal conditions, the skin contains many different types of nerve endings that distinguish between different temperatures, different types of mechanical contact such as vibrations from a cell phone and movement of hairs, and, importantly, painful stimuli.
The researchers found the presence of sensory nerve endings on the small blood vessels and sweat glands embedded in the skin.
"For many years, my colleagues and I have detected different types of nerve endings on tiny blood vessels and sweat glands, which we assumed were simply regulating blood flow and sweating. We didn't think they could contribute to conscious sensation. However, while all the other sensory endings were missing in this unusual skin, the blood vessels and sweat glands still had the normal types of nerve endings," said Rice.
"Apparently, these unique individuals are able to 'feel things' through these remaining nerve endings," Rice added.
The new study is published in the journal Pain.