Jan. 20, 2016 -- Scientists are questioning whether people who are unwittingly exposed to ultrasound in everyday situations could face health risks.
Little is known, they say, about how we might be affected by ultrasound -- sound beams given off by devices like door sensors, loudspeakers and overhead speaker systems.
Nausea and Fatigue
Scientists based at the University of Southampton in the United Kingdom found that people are being exposed more and more to ultrasound in places such as transit stations, museums, schools, and sports stadiums, in which there have been complaints of nausea, dizziness, migraine headaches, ringing of the ears, and fatigue, they say.
Such reports have been echoed for 40 years by people in the workplace, particularly those exposed to ultrasound from cleaning and drilling devices.
The new study is published in the journal Proceedings of the Royal Society A.
Some experts have their doubts about the research, with one saying there is little evidence that "ultrasonic pollution" is a danger.
Leighton says his main concern is to see new research leading to new guidelines on airborne ultrasound.
The current guidelines on it shouldn’t apply to the general public, he says, because the majority refer to exposure at work, “where workers are aware of the exposure, can be monitored, and can wear protection,” Leighton says in a statement. “Furthermore, the guidelines are based on the average response of small group, often of adult males.”
The guidance is based on evidence collected more than 4 decades ago by researchers, he says. It was used to come up with early guidelines on ultrasound exposure, because there wasn’t enough evidence to say more, he says.
To measure ultrasound levels, Leighton and his team used smartphones and tablets equipped with an app. They measured the levels in several public buildings while they were occupied by hundreds of people.
The team found that people were being exposed to ultrasound levels in excess of 20 kHz, which is the threshold laid down by current guidelines. Twenty kHz is the upper range of human hearing.
"Individuals who are unlikely to be aware of such exposures are complaining, for themselves and their children, of a number of negative conditions,” Leighton says.
More research on the subject is needed, says Martin Coath, associate lecturer at Plymouth University.
"Ultrasound is a silent companion to everything we do," he says. "We make it when we rub our hands together or when we wrap food in aluminum foil -- in fact when we do pretty much anything.
"The degree to which we should control processes that make a heck of a lot of ultrasound at high enough levels to make people uncomfortable or unwell needs to be debated, and for that we need loads more evidence than we have."
Jan Schnupp, professor of neuroscience at the University of Oxford, is skeptical about the findings. "While the author is correct in saying that we perhaps know less than we ideally would like about ultrasound levels in our environment, we nevertheless do know enough to be able to be fairly confident that it is very unlikely to be a significant health hazard to humans," he says.
Since the invention of the fluorescent light bulb, billions of people have been exposed to the ultrasound they emit without ill effects, Schnupp says.
"My advice would be to worry about the sounds you can hear, enjoy loud music (like alcohol or calorie-rich foods) in moderation, exercise occasionally, have fun, and leave it to the hypochondriacs to worry about the potential harms of ultrasound exposure."