Research project: Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?

Members of the public, and workers at these locations, are being exposed without their knowledge. Spectra and levels are recorded using calibrated equipment in the paper that can be downloaded for free from The Royal Society paper (click on the pdf symbol to get the paper). However Appendix A of that paper, and visit the video How a smartphone or tablet computer can monitor for ultrasound in air, show how members of the public can take their own uncalibrated measurements using smart phones and tablet computers. 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 below 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 visiting the Tim Leighton Instagram page.

There are guidelines for how much exposure workers -not members of the public- can receive for ultrasound in air, but these show very large variations, disagreeing by factors of up to 3 million in terms of the intensity to which these workers can be subjected. There is only one guideline for public exposure. However all these guidelines are based on inadequate evidence, looking at data from too few people, and making assessments based on averages of the people studied. Most of these people were adult males, many worked in service or industry, and so was not sensitive to:

• The existence of people who are more sensitive than the average;
• The existence of subgroups within the general population (such as children) who may be more sensitive to adverse effects from ultrasound in air compared to the average of the people involved in testing.

However the guidelines issued by many countries and institutions have gained unwanted credibility because they appear to agree. This agreement is illusory: there is so little basic research that in issuing ‘new’ guidelines, organisations and countries have copied existing guidelines, giving the appearance of validating them by implying an independent consideration of new evidence.

Furthermore, whilst some manufacturers and studies purport to measure the amplitudes of fields to which people are exposed, the standards by which sound level meters are built mean that at 20 kHz (usually taken as the borderline between ultrasonic and audio frequency sound) these “measuring devices” can underestimate the intensity of the ultrasonic field by any amount at all, and still meet the standard. Therefore our entire history of recorded levels of ultrasound by such instruments is called into question.

Moreover, the scenario for exposure considered by the basic research, and guidelines, is typically someone working with an ultrasonic cleaning bath in a noisy industrial setting where workers have limited and monitored exposure to intense acoustic fields, can wear hearing protection, and they, their employers and medical carers know they are exposed. They were not designed for current exposures of members of the public who at are in ignorance of such exposures. Today people are exposed by public address systems which have ultrasonic tones that are supposed to be inaudible to humans, and there are companies that claim to embed ultrasonic signals in TV adverts so that the phone in your pocket can monitor what adverts you watch even when you might think yourself anonymous ( e.g. at a hotel or Internet café). Such unexpected exposures add to the more prosaic set of airborne ultrasonic tones we might expect, e.g. from pest scarers, automatic door opening systems etc.

A recent paper (Royal Society paper to download for free) shows how members of the public are in fact able to detect such ultrasound using some types of smartphone and tablet computers (visit How a smartphone or tablet computer can monitor for ultrasound in air for an explanatory video and read Appendix A of the paper which is available Royal Society paper).

There has been insufficient research to confirm or deny whether ultrasound is in fact the source of adverse effects people might feel, but recommendations are included in the paper (visit Royal Society paper to download for free) regarding the testing of people and the obligations on manufacturers and those who deploy such devices.

Given 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. This unfunded study lacked the resources to conduct randomized double blind human experimentation to see whether the individuals who might be sensitive to ultrasound in air in public spaces do indeed respond to exposure with such symptoms. Conducting such tests is a long-term goal.

We have an email address (hefua@soton.ac.uk to send a message ) to which queries can be addressed but please be aware we have no funding to staff this and if the number of emails sent to it is large we may not be able to reply to all the enquirers...

IMPLICATIONS FOR ANTIMICROBIAL RESISTANCE

Some members of the public who claimed to have pain in the ear caused by ultrasound in air, also claimed to have had ineffective antibiotic prescribed to treat it. Adverse effects from ultrasound in air do not feature in NICE guidelines so cannot be used in differential diagnosis, a situation that could lead to inappropriate use of antibiotics (which has wider implications – NAMRIP: Innovation and approach diagram), although the extent to which this has happened is not known, and these are currently only anecdotal reports.

Therefore the importance of this study may extend beyond the avoidance of adverse symptoms listed above (ear pain, headache, migraine, nausea, fatigue, dizziness etc.), and impinge upon the issue of AntiMicrobial Resistance. In his paper, Prof Leighton noted that ‘the lack of evidence means that adverse effects from airborne ultrasound are not included in any of the relevant NICE publications that support differential diagnoses’. He added for this webpage that: ‘The possibility that antibiotics are prescribed for ear pain caused by this non-microbial agent is an interesting, but as yet unproven, possibility. It is no bad thing to wonder for a moment at the extent of the list of conditions for which antimicrobial agents are inappropriately used. Good stewardship of current and future antimicrobial agents is vital to avoid twin catastrophes in healthcare and food production (visit The Conversation website for details). Good stewardship includes accurate diagnosis and appropriate therapy, avoiding the use of broadspectrum antibiotics where a narrow spectrum one would suffice, and avoidance of any antibiotics where none would remedy the condition presented. That is a key role of NAMRIP (the Network for AntiMicrobial Resistance and Infection Prevention)’.’

WHAT ARE THE ARGUMENTS AGAINST?

The paper does not claim every complaint of ill effect from ultrasound in air is verified. It argues that we cannot continue dismissing them all. The following arguments have been made to counter the paper. Since they are the same arguments that have been made by professionals to those who report adverse effects, they bear repeating here.

[1] ‘The vast amount of ultrasound just bounces off the skin so people cannot be affected’. It is true that the vast amount of energy in any airborne acoustic wave (ultrasonic or audio frequency) bounces off the skin, with very little energy penetrating. This is why we do not try to hear with our skin but evolved ears instead. Prior to this paper there has been no proposed mechanism for the generation of fatigue, nausea, headaches from ultrasound in air, and the above argument relies on the unstated assumption that the ear plays no part in the process. Section 4 of the paper proposes a mechanism that does involve the ears, but this is simply a straw man. However its existence means that we cannot dismiss claims of adverse effects if we state that the role of the ear must be ignored, and we can only rely on the miniscule penetration of the acoustic wave from the skin to cause any effect.

[2] ‘People cannot hear much above 18 kHz’. This includes the unstated assumption that if you cannot hear a sound it cannot cause you adverse effects, This assumption is not proven, and the strawman mechanism in section 4 of the paper does not require hearing for adverse effects. Therefore all claims of adverse effects cannot be dismissed using this unproven assumption. Furthermore, a proportion of the population can indeed hear frequencies above 20 kHz, as figure 4 of the paper shows. Indeed, the fact that a minority are sensitive produces social questions, for example if a grandmother carries a baby into a field they find benign, but the child might not, and the grandmother is unaware of any exposure at all.

[3] ‘Some people imagine ill effects when they are not caused by any physical mechanism’. This is true throughout medicine but it does not mean that all claims of ultrasound in air can be dismissed.

[4] ‘The measurements in figure 1a of a 20 kHz signal are likely to be an artefact produced by the sampling frequency of the iphone’. The signal disappears when the finger is placed on the iphone microphone. Furthermore it was replicated in independent microphone and data acquisition systems that were used to measure the same signal, and also disappeared from those when a cover was placed over the microphone, and returned when the cover was removed.

[5] ‘A lot of ultrasound is generated by the environment around us: fluorescent lights etc.’. The question here is one of intensity. We measured areas with low levels of ultrasound, some with no detectable ultrasound, and some with high levels of ultrasound, depending on the sources present and the distance from them.

[6] ‘The amount of physical energy in much airborne ultrasound is very small.’ This is also true of audiofrequency sound, but we can produce uncomfortable levels of it. The issue here is that we have evolved structures to be especially sensitive to acoustic stimulation (our hearing system).

[7] ‘There is not much new data in the paper [at http://tinyurl.com/hohu3wq ].’ Apart from the new evidence showing public exposure (with calibrated levels), this is true: new data was not what was needed at the time (nor was it affordable). New data has been trickling in for the last 50 years, but has not affected the complacency that had crept in over the guidelines, or the standards of accuracy we require of our instrumentation, or the uncritical way in which we translate procedures used at audio frequencies to deal with VHF and ultrasonic ones. We first needed to create an environment in which what we do now is questioned. A dataset that is significant enough to draw up new guidelines will take testing of several thousand volunteers, including children (because public exposure has been proved), generating adverse effects in an ethical way (an ethical approach could not expose an volunteer for more than a very limited time between rest days). That will take extensive funding and years of research, and indeed may not be possible to conduct. The current paper might produce a more rapid and sensible resolution by generating questions to bring the stakeholders together to a reasonable solution on guidelines in the short term, based on a much smaller dataset but an attitude of questioning and cooperation.’

For more information visit my The Royal Society paper

Acknowledgements.

Apart from a contribution to equipment costs by the Colt Foundation (for which we are grateful), this work was unfunded, and therefore, a large number of volunteers were vital to completing this multidisciplinary study, and credit to them that it was completed in a few months. To be sure of the levels recorded in figures 1 and 2, several independent measurements were made of the ultrasonic field from students Fabio Casagrande Hirono and Mengyang Zhu, and from the NPL’s Ben Piper, each operating their own independent equipment and measurement systems. Ben Piper and Richard Barham of NPL assisted with calibration, as did ISVR Consulting, who loaned us equipment. The author is very grateful to Ben Lineton and Sian Lloyd Jones for audiological advice, Sian also for providing an independent audiological detective to assist in tracing though often obscure and difficult-to-find records of the tests on which some current guidelines are based. All the above, plus Ben Lawton and Carl Verschuur commented on sections of the draft. The author is grateful to Erika Quaranta for undertaking all the modelling requested by the author of the interaction of sound and ultrasound with the pinna (figure 6); and to Richard Jackett (NPL) for supplying figure 5 at the author’s request. The author is grateful to Paul White for advising on signal processing and the statistics of appendix C; Andrea Wolff for interpretations and guidance on German law; Su Blandy for helpful advice on how a clinician interacts with NICE guidelines. The author is grateful to two school students on work experience placements, specifically Laura Overton-Hore and Tim Scrase, for their assistance during field tests, taking notes on sites locations and metadata, and for their assistance in checking transcriptions of notes and data. The author is grateful to Clare Chapman, Rhiannon Leighton and Gareth Lloyd Jones for proof-reading the manuscript.