Is Wetness Just an Illusion?

Whether feeling humidity, sweat or a damp towel, encountering stimuli that feel wet is nothing out of the ordinary. But while it may seem simple, feeling that something is wet is quite a feat because our skin does not have receptors that sense wetness, according to a new study. So how exactly do you know what wet feels like?

A team of scientists from Loughborough University and Oxylane Research recently decided to answer that very question.

It turns out that what we perceive as being wet is more just a "perceptual illusion" in our brains telling us that something is wet based on our past experiences with things such as water and sweat. So what has kept us this whole time from accidentally sitting on a wet seat or walking through a puddle?

The researchers suggest that our wetness perception is tied to cold temperature and sensations such as pressure and texture. In addition, sensory nerves called A-nerve fibers, which carry temperature and tangible information from the skin to the brain, are also shown to play a part.

To test the theory, lead author Davide Filingeri and his team exposed 13 healthy males, all college students, to various wet stimuli, including things that were warm, cold or room temperature.

Interestingly, it seemed that volunteers responded more to wet stimuli when it was at colder temperatures compared to when at warm or room temperature. They also discovered that when they expanded the area of the blood pressure cuff, which numbed nerves, volunteers were less sensitive to wetness. Even more fascinating was that hairier parts of the body are more sensitive to wetness than those parts without hair, like fingertips.

"Based on a concept of perceptual learning and Bayesian perceptual inference, we developed the first neurophysiological model of cutaneous wetness sensitivity centered on the multisensory integration of cold-sensitive and mechanosensitive skin afferents," the research team wrote in the Journal of Neurophysiology. "Our results provide evidence for the existence of a specific information processing model that underpins the neural representation of a typical wet stimulus."