Researchers examined skin samples from two European men with congenital absence of or insensitivity to pain. People with this condition have few nerves in their skin, and feel very little if any pain, temperature change or vibration.

What drew researchers to these two individuals was their excessive sweating. Although otherwise normal, they were sweating three to eight times more than usual.

“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,” says Frank Rice, lead author of the study and professor of neuroscience at Albany Medical College. “We didn’t think they could contribute to conscious sensation.”

The sensation isn’t like the feel of touch. It’s a much subtler feeling, like hearing background music from a party next door. “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 explains.

The first man had never experienced pain, and could not sense water temperature, skin burns, or fractures. Although being slightly more receptive to sensation than the first, the second man also could not sense second degree burns, and had had several fractures of which he was unaware. He did report being able to feel ticklishness and itching as a child.

Despite a lack of nerve tissue in the skin, both men had sensitive tissues in the sweat glands—enough to tell if things were touching them, whether things were rough or smooth, or whether some things are warm or cold.

“Since only the innervation to the blood vessels and sweat glands is intact,” authors write, “the thermal detection from deeper tissues and the blood may be misperceived as though there is a continuously high surface temperature, thereby eliciting excessive sweating.”

Researchers believe the fact that the two subjects maintained the ability to sense some sensations suggests that vascular afferents, such as blood vesicles, may contribute to conscious touch awareness.

Read the study in the online journal, Pain.