New wearable sensor tracks scratching to measure itch

April 30, 2021
If this picture makes you itchy, a new sensor can track when you scratch. (Pixabay/WikiImages)

If this picture makes you itchy, a new sensor can track when you scratch. (Pixabay/WikiImages)

Scientists have devised a more objective way of measuring itch with a wearable sensing technology that tracks how often people scratch themselves and accurately distinguishes real scratching from similar motions, potentially giving physicians better information to help patients with eczema and other itch-related conditions find relief.

In a study published Friday in Science Advances, the device is described as an "advanced acousto-mechanic sensor" that captures the vibrations of people scratching their skin. Corresponding author Steve (Shuai) Xu, a dermatologist and physician-engineer at Northwestern University in Illinois, told The Academic Times that the sensor is designed to help physicians determine which medications really work for treating skin conditions, the severity of which often go unrecognized. "Itch gets no respect," he said. "Pain you know is serious and important to treat, but itch is kind of like, 'Eh.' But itch is a really debilitating symptom."

People living with atopic dermatitis — also known as eczema, a condition experienced by nearly 18 million Americans, mostly babies and children — are prone to major sleep disturbances that degrade their overall quality of life. "All of the itching leads to sleep problems, and you can imagine what kind of suffering it causes," Xu said. "Think about kids trying to focus in school and develop their brains."  

Currently, the most common way clinicians measure itch is simply asking patients how bad it is. "I knew we had a problem quantifying itch in an objective way," Xu said. "The best analogy is pain: To quantify pain, they give you a comic book, and you pick which crying face best represents you, right? Itch is kind of the same thing; they're both very difficult to quantify." 

In research settings, infrared camera recordings are the gold standard for objectively measuring itch, providing direct visual observations of how much people scratch themselves at night, Xu said. But that method is not scalable or user-friendly, as people generally don't like being visually recorded while they sleep. The Apple Watch also has an itch tracking-app, but it's limited by the sensor's tracking of wrist movement. "If you think about scratching with your fingers, your wrist is not really moving," Xu said. "A lot of people scratch with just their fingers." 

Enter the team's new soft, flexible sensor. Designed to be worn continuously, it looks like a thick Band-Aid. It's equipped with a seven-day battery and wireless charger, safe to be worn in the shower, and readily paired with iPhone and Android apps that track users' scratching habits. It is also designed to avoid false positives — in other words, miscategorizing non-scratching motions as scratching because they might look superficially similar.

"If you scratch your hand and you put your ear really close to it, you can hear there's sound of scratching, as well as motion," Xu said. "Our sensor actually captures the vibration that is generated from scratching, and that allows us to be more sensitive and specific to scratching itself." If you make a scratching motion in the air without touching your skin, for example, the sensor does not record the movement as a scratch. Using a novel algorithm, it picks up both low- and high-frequency signals from the body, separating the vibrations of scratching from background noise. 

In a clinical trial, 11 children living with atopic dermatitis wore the sensor for a combined total of 46 nights. Comparing the results against "cold, hard infrared recordings," Xu said, the researchers found that the device identified scratching movements with 99% accuracy. He believes the duration of the experiment compensated for the relatively small number of subjects. "Of studies that have looked at scratch, we're one of the largest, if not the largest, in terms of total duration because some of these patients generated 4 or 5 nights of data," he said. "Since then, we've done [studies with] more than 50 people, and I will say that the performance has been the same, if not better." 

The paper is the first to validate scratching behavior in children, Xu said, which is important because atopic dermatitis primarily affects young people. But the researchers are studying the sensor's efficacy in adults as well. They believe the sensor could be applied to a range of conditions — renal disease, liver failure and blood cancers, among others — that are often associated with severe itching. 

A commercial product could soon be available to dermatologists and patients, Xu said. His team is planning on submitting the new sensor for approval from the U.S. Food and Drug Administration within the next few months, and he anticipates that the product will roll out globally by the end of the year. He hopes the groundbreaking device will alleviate the suffering of people with skin conditions and other itch-inducing diseases. "It's not just itchy skin; measuring it isn't just cute," he said. "This is real clinical suffering."

The study, "A skin-comfortable wireless sensor to objectively quantify symptoms of pruritus," published April 30 in Science Advances, was authored by Keum San Chun, University of Texas at Austin; Youn J. Kang, Morgan Nguyen, Brad Lee, Emily Allen, Hope Chen, KunHyuck Lee, Hyoyoung Jeong, Yoonseok Park, Alvin W. Li and John A. Rogers, Northwestern University; Jong Yoon Lee and Ha Uk Chung, Northwestern University and Sibel Health; Lian Yu, University of Illinois; Xiaoyue Ni, Northwestern University and Duke University; Peter A. Lio, Chicago Eczema Center; Anna B. Fishbein, Ann & Robert Lurie Children's Hospital of Chicago; Rachel Lee, Han Heul Jo, Jungwoo Kim and JooHee Lee, Sibel Health; and Amy S. Paller and Steve (Shuai) Xu, Northwestern University and Ann & Robert Lurie Children's Hospital of Chicago.

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