No sweat

Did you know we don’t have a receptor in our skin for wetness? It’s a sensation we take for granted – an experience our brain picks up from other cues, such as temperature and touch. Pioneering research is exploiting these facts to influence everyday product design, from nappies to deodorants.

We all know what it feels like to be wet. It’s often closely associated with a feeling of cold. But what is the science behind that feeling?

It’s not as simple as you might think.

Dr Davide Filingeri, Associate Professor in Skin Health within the School of Health Sciences, is dedicating his career to understanding how our brain tells us something is wet, considering we don’t have a receptor for wetness in our skin as we do, for example, for temperature and pain.

“You can play with the brain,” said Davide. “Wetness is one of the most common sensations we experience, so people don’t question it. You can trick your brain to feel wet when something is not wet, or trick it to feel dry when in fact something is wet.

“If you are sitting on a metal chair with bare skin, you might jump up feeling wet when really it’s just the cold of the metal that cools the skin very quickly. Or, if you wear a latex glove and put your hand into water and take it out again, you will probably feel wet on your hand even though there is no moisture in contact with your skin.”

Davide’s background is in thermal physiology and temperature regulation, and understanding some of the basic mechanisms that allow us to regulate body temperature but also sense the external environment. This has led to ongoing research, which started about a decade ago, into how we detect changes in temperature and wetness.

In 2017, Davide founded Thermosenselab, based within the Skin Health Research Group, which specialises in research into skin sensing.

“We have discovered that the body uses temperature and touch cues to make sense of wetness on the skin,” explained Davide. “We have developed a physiological model that predicts what physical cues induce a sensation of wetness, which manufacturers of products that deal with wetness are interested in applying to improve the design and comfort of their products.”

Enterprise collaborations Davide’s research has sparked a series of enterprise collaborations with consumer goods manufacturer Procter & Gamble (P&G), as well as with major sports clothes manufacturers.

An initial project with P&G developed new knowledge on the thermal, mechanical and visual inputs that drive skin wetness sensing. P&G used the results of this to inform the design of more comfortable nappies.

“The aim of the project was to model the interaction of a finger as it slides along a wet nappy and understand what sensing cues people use to sense wetness,” said Davide. “Temperature or friction could change the sense of wetness, regardless of the amount of wetness in the nappy. You can trick the brain to feel wetness when there is no wetness, and vice versa.”

He has also worked closely with sports clothes manufacturers to assess sports apparel design and comfort in specific populations, such as female athletes.

“We have done lots of research into how you detect temperature across your body,” he said, “which is relevant to people producing sports clothing because they can use this knowledge to design garments that take into account the different sensitivities across the body. Making garments more breathable in certain areas, or warmer in areas that are prone to getting cold in cooler temperatures, for example.”

Sweaty business A new project, due to start in 2022, will seek to understand the biophysical and perceptual mechanism of skin wetness sensitivity of the underarm, to inform the design of more comfortable antiperspirant deodorants manufactured by P&G.

Davide said: “The idea is still to try to understand better the basic sensory mechanisms that allow us to detect wetness, this time in the underarm area.

“Antiperspirant deodorants are designed to reduce the amount of sweat that you produce – they are used to protect against wetness and for comfort reasons. If we can understand how the sensations of wetness vary between men and women, or vary depending on age, or vary for women depending on the stages of the menstrual cycle, we can try to convey this knowledge to product design and optimisation.”

The research team will recruit participants and use methods including quantitative sensory tasks, where specific stimuli are applied to the skin that can be controlled in terms of temperature and wetness, then asking people to report what they feel. Another method will involve presenting participants with a variety of stimuli with different degrees of wetness on them, and asking if they find them to be wet. “Then we can determine the minimum amount of moisture they can detect,” explained Davide. “It allows us to assess the local sensitivity to a wet stimulus.”

The team will also use the climatic chamber at the NIHR Wellcome Trust Clinical Research Facility, where they can control air temperature and humidity to stimulate sweat production. Experiments here will determine how people sense sweat, to what degrees they sense it, and what the effect on comfort is of adding interventions such as antiperspirant.

Anticipating the potential outcomes of this project, Davide said: “Based on the findings of this research, there might be implications for the chemicals that are used in products to moderate sweat production and sweat sensation. As a result of this research, perhaps we will see more user-centred products. Perhaps more age-specific or gender-specific deodorants. Or perhaps even products designed for different stages of the menstrual cycle.”

Body maps to show regional differences in thermal sensitivity to warm, neutral and cold wet stimuli in males and females pre- and post-exercise

For further information, visit: www.thermosenselab.com