Health Effects of Ultrasound in Air (HEFUA)

HEFUA promotes the Public Scientists: This iPhone spectrogram was taken by a member of the public after she experienced nausea and ear discomfort in a public concourse. It shows an ultrasonic tone with a frequency around 20 kHz, pulsing on for around 10s, then off for about 10s (the levels are uncalibrated, and the level of interference from electronic noise is unknown). Such tones are commonly used to monitor the integrity of public address systems in shopping centres, railway stations, public buildings, department stores and stadia.

[1] Synopsis: HEFUA is the UK consortium (encompassing researchers, clinicians, policymakers, and the public) that addresses the fact that humans are being increasingly exposed to ultrasound in air through commercial devices. There is insufficient understanding of how these devices affect health, even when exposures are known. Exposures are difficult to assess: indeed measurements of the device outputs could not have been traced to measurement standards because these are only just emerging. There is clearly a knowledge gap, requiring a multidisciplinary discussion. HEFUA is a partner organization within the University of Southampton Strategic Research Group into Population Heath.

[2] Findings to date:

(a) A result by Professor Leighton of his investigations in to the phenomenon was published by the Royal Society on guidelines, standards, emitters and the possibility of adverse effects on humans as a result of ultrasound in air from commercial devices is available for free click clicking the PDF icon at the web page here

(b) A follow-up article was published by the Royal Society in 2017.

(c) A video showing how smart phones and tablet computers can be used by members of the public to detect ultrasound in air is available here (further explanation is given in Appendix A of this paper). We invite you to take such measurements and post them (with details of where and when the recording was taken, with what device, app and settings) into the feed found here by following us on Instagram @Ultrasonics_at_Southampton and post your own using the hashtag #UltrasoundInAir. The complete feed to date can be seen by clicking here .

(d) A news feed can be found at the base of the page.

[3] Purpose of HEFUA: We are concerned that there is currently a paucity of evidence that can be scientifically used to assess the claims by members of the public that they, or their children, experience adverse effects as a consequence of exposure in air to ultrasound (frequencies in excess of 20 kHz) and very high frequency sound (15-20 kHz). The data are sparse, and the specialized techniques and equipment for measurement and calibration in this environment are not widely available. 

Set against this, there is increasing objective evidence that incidental exposure to such fields is becoming more common and widespread, e.g. through the use of such high frequency sounds  for pest deterrents, and in public spaces as part of the usual operation of some automated doors, fire alarm systems, etc.  This group will meet to understand the issues and challenges, and devise strategies to obtain objective and rigorous knowledge base to assist the community, manufacturers, and policymakers. The aim of HEFUA is to assist both the public and the manufacturers by removing the knowledge gap.

[4] Background: In 1984 the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) published a set of interim guidelines limiting human exposure to airborne ultrasound (“Interim guidelines on limits of human exposure to airborne ultrasound”, Health Physics, Vol. 46, No. 4, pp. 969-974, 1984). In 2013 it decided that these brief guidelines needed updating and revising. Almost none of the commercial devices that currently expose humans to airborne ultrasound were present in 1984. There is no accompanying research programme to inform the revision of the guidelines. An archive of documents can be found at the base of this webpage.

[5] Social implications of commercial ultrasonic devices: Humans are becoming increasingly exposed unknowingly to ultrasound in air through commercial devices (e.g. pest-scarers on buildings, exhibition stand ‘acoustic spotlights’ etc). Some people are being exposed in their homes and public spaces on a daily basis. The reliance on the adage that sound with frequencies in excess of 20 kHz is safe to use because humans cannot perceive it, does not take into account (i) the scientific reports of ultrasonic health effects, or (ii) the presence of particularly sensitive individuals in the population. A single device could expose a diverse population e.g.:

  •  a grandmother, unaware of a high frequency field, could take a toddler into a distressing acoustic environment;
  •  a guide dog could become distracted, irritable or distressed whilst supporting a visually impaired person;
  •  students at a school or patients at a hospital near a pest deterrent could be more vulnerable than the person installing the sound source and have no option to move away from the environment. 

Pest scarers on roof tops or in gardens, and the use of ultrasound signals to monitor the integrity of sound reproduction systems in public spaces expose a diverse population. It may well be that the exposure levels are sufficiently low, even for children, to generate no adverse effects, but measurements are extremely scarce and could not have been traced to standards, which are only now being formulated. Across the UK members of the public (e.g. tower block tenants) attribute adverse health effects to exposure from such commercial devices. This might be misguided, psychosomatic, or evidence of a causal physical result of the exposure. There are too many unknowns currently, and the price of continuing in ignorance could include:

  • unwarranted damage to the industries manufacturing these devices;
  • ultrasonically-mediated health effects; or
  • failure to reassure distressed members of the public.

If a researcher were to purchase such a device and wished to expose humans to it in a laboratory, they would require ethics approval and risk assessments, and there is not the scientific basis to produce either. The importance of the issue comes from several sources. If current airborne ultrasonic exposures are proven to be safe, manufacturers can develop products from a secure knowledge base, and symptomatic individuals can be assisted in identifying the true cause of problems and be appropriately assisted. If current airborne ultrasonic exposure is found to be hazardous to human health, regulation will be required to control future devices, the deployment of current devices must be checked to ensure protection of the population, and symptomatic individuals can receive directed support. If safe exposure levels can be determined, and appropriate measurement and calibration procedures put in place, then this will protect not only a growing industry but the health and wellbeing of people, especially children.

[6] The special case of Mosquito: The installation and use of ‘Mosquito’ devices continues to be unregulated. These devices do not emit ultrasound (as the devices discussed above do), but emit intense sounds at around 15-18 kHz with the specific intention of creating a distress response in young people and thereby discourage them from ‘loitering’ in the vicinity of the device: in the words of the manufacturers, Compound Security Systems Ltd., “So, you're having problems with kids and teens? If you want to reclaim your right to a peaceful existence, buy your Mosquito Anti-Loitering Device now!”. Individual householders and owners of business premises owners can install the devices.

The device operates on the principle that people more than, say, 25 years old will have lost sensitivity to these irritating Very High Frequency (VHF) signals, but ignores:

• The effect on animals, including Guide Dogs;
• The effect on very young children carried near the device by parents;
• The effect on children with pre-existing conditions that make them especially sensitive (autistic spectrum disorder, hyperacusis, Williams syndrome etc.);
• The health effects of children who cannot avoid long term exposure (e.g. because of their residence, the daily route to school etc.);
• The lack of research to understand the potential effects of VHF and ultrasonic signals on individuals who cannot hear them;
• The fact that the Mosquito fails as a substitute for investment to provide appropriate safe places (e.g. youth clubs) for children to meet, since the device can displace children to more hazardous areas.

[7] The citizen scientist: We are interested to hear your reports (though apologize if there is a delay replying as we are a small volunteer workforce).  If for example you want to search for ultrasound in air on your phone, using a spectral processing app, ensure the phone can acquire the data at sufficiently high frequency (the sample rate must be over 40,000 Hz (preferably over 48,000 Hz), and the Fast Fourier Transform set to the maximum number of samples allowed. If in doubt, set everything to maximum! Detailed instructions are given at the end of this section, in green.

Take a note of those settings, and the make, model and (if possible) operating system, and details of the spectrum analyser app. 

If you detect a signal, record it as a picture. If you can, use a function to show the frequency and dB level at the ultrasonic signal. It is very important that you then check that it is not due to electrical interference.

You can do this by recording in exactly the same way, with the same settings, but first covering up the microphone with your finger (check on the web which microphone you need to cover – many phones have two different microphones, one for voice and one for functions like video recording, and that is the one you need to cover). 

Check that the level of the signal decreases (e.g. goes from red to yellow in the spectrogram) as you put your finger over the microphone, and dos the reverse when you take it off. That proves this is an acoustic signal, and not electrical interference.

Save the picture for us. Send both pictures, the record of your phone and app and their settings, and a description of your location (with GPS if possible, and info about the sound source if you have it) using the button at the top right of the page. 

Basic instructions for looking at the frequency emissions up to around 22 kHz using SpectrumView application on iPhone:

Install the Spectrumview application (free - does not allow recording or much detail) or SpectrumViewPlus (cost of a few pounds, allows recordings to be taken and zooming in on detail).

Towards the bottom left hand corner of the screen is a microphone/pause toggle button. This starts/pauses observation of the current sound in the environment.

The application has a number of buttons at the bottom:

Spectrogram, Spectrum Analyser, Recording, Playback, Settings, Help, About.

Go to the Settings tab, and then set the following settings:
  • Audio Sample Rate (Hz) to maximum setting : 48000
  • FFT setting to maximum: 13 (8192)
For the best results, check that the following are set:
  • Spectogram gain (dB) is set to 0.0dB 
  • Use Automatic Gain Control (Apple) should be On.
Then back on the Spectrogram and Spectrum Analysis tabs, you should be able to see frequencies up to 22-24 kHz and note any very high or ultrasonic frequency sound emitted up to this figure. Beyond these frequencies, specialist microphones would be needed.

[8] Has this anything to do with ultrasound in baby scans? No, foetal scans represent a very different form of ultrasonic exposure,  using frequencies that are more than 20 time higher than those we study here, and which involve entirely different safety considerations. 

Click here to email HEFUA

“The start of the 21st century has seen a proliferation in the sale and deployment of devices that expose humans to ultrasound in air in public and residential spaces. Given the complaints from the public, and the difficulties in measurement checks on such fields, our ignorance on health effects should be a cause for caution and research, not a cause for increasing sales and deployment. Ultrasound undoubtedly can bring benefits. We want to get the best out of ultrasound, but safely, protecting everyone: manufacturers, users, policymakers and the public.”

Professor Timothy Leighton FREng FRS 
(Chair of HEFUA; 
Institute of Sound and Vibration Research, University of Southampton)

“There have been reports of adverse effects of airborne ultrasound on humans for many years, but only recently have the measurement standards been established to enable airborne ultrasound fields to be measured reliably. Now that sources can be quantified, research to understand the link between exposure and claimed symptoms can accelerate. Measurement science is just one facet of this multidisciplinary research which ultimately requires collaboration between medical, engineering and social science fields and increasingly, input from citizen science.”

Dr Richard Barham
(Principal Research Scientist,
Acoustics and IR Division,
National Physical Laboratory UK)

Useful links:

Email HEFUA 

Scientific references:

These can be uploaded from the base of this page.