A study found that high exposure to airborne ultrasound from loudspeakers, public address systems and door sensors can cause health problems. These sources can be found in many public areas such as museums, libraries, sport stadiums, railway stations and even schools.

Health problems arising from increased exposure can lead to migraine, fatigue, dizziness, nausea and tinnitus in most people. A study from the University of Southampton found that many people are being exposed to airborne ultrasound in public areas without knowing it. Ultrasound refers to sound at exceedingly high frequencies, which is commonly beyond 20 kHz that is beyond what most people is able to hear.

Study author Professor Tim Leighton used a smartphone/tablet app to monitor increasingly high frequency of airborne ultrasound in various public areas wherein people have reported feeling dizzy, sick and tired. Reports also said they experienced ear pressure, vertigo and recurring headaches.

The collected airborne ultrasound data were then calibrated using up to three audio data and microphone systems. Leighton found that the public was unknowingly exposed to more than 20 kHz of very high frequency/ultrasonic fields (VHF/US) levels.

The findings suggest that for people aged 40 to 49 years old, one in 20 individuals have hearing limits that are 20 decibels (dB) more sensitive at 20 kHz than those of people aged 30 to 39 years old.

"Moreover, five percent of the 5 to 19 year age group is reported to have a 20 kHz threshold that is 60 dB more sensitive than the average for the 30-39 year age group," said Leighton.

Leighton added that the existing research and guidelines for work safe levels are not enough to deal with the present rate of ultrasound exposure the public is unknowingly receiving. Existing guidelines refer to occupational exposure to ultrasound where the workers, who are highly aware of the situation, can take safety measures. The current guidelines were also created based on the median response of a small study group composed mostly of adult males in the 1960s.

Leighton stressed that is crucial for people to trace the real cause of their health symptoms even if its linked to very high frequencies of ultrasound or not. The study is published in the journal Proceedings of the Royal Society A on Jan. 20.

Photo: Charlie Brewer | Flickr