January 20, 2016

expert reaction to ultrasound and health

A study published in the journal Proceedings Of The Royal Society A has reported that the public is exposed to high levels of airborne ultrasound, the majority of which is from occupational exposure.

Prof. Jan Schnupp, Professor of Neuroscience  at the University of Oxford, said:

“I have to declare that I am rather sceptical about this.

“It is true that there is a lot of ultrasound generated by appliances in the modern world. Fluorescent lights, for example, can emit quite a lot of sound above 20 kHz. I can also imagine that these ultrasounds might be annoying to pet dogs, cats or rodents who tend to have much more sensitive hearing at much higher frequencies than we do.

“However, the amount of physical energy in these ultrasounds is absolutely tiny, and almost none of those tiny amounts of sound energy will penetrate from the air into our bodies. It will just bounce harmlessly off our skin. Such a phenomenally tiny amount of ultrasound energy from the air will penetrate our bodies that it is quite hard to envisage it could do any serious damage.

“At the same time, literally billions of people have been exposed to ultrasound from fluorescent lights for many years and by and large living longer and healthier lives than their parents’ generation.

“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.

“My advice to 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.”

Prof. Jonathan Ashmore FRS, Bernard Katz Professor of Biophysics at the UCL Ear Institute, said:

“This study has clear scientific deficiencies.

“There is little new data here, and that which there is (e.g. Fig 1) is not well controlled. When you see a really narrow band sound as is shown near 20kHz the chances are that it comes from the digital sound system, as many CD players – and even iPhones – sample at 42-44kHz which is remarkably close to 2x what is reported! Public libraries? Air conditioning systems are also liable to whistle, so the wobbles you see in the trace can easily be the effect of doors opening, people moving etc.

“Physiological evidence very strongly suggests that the ear does not pick up any airborne sounds much above 18 kHz, certainly in adults. If there are indeed real experimentally reproducible physiological effects then indeed more research needs to be done, but it might be more profitable to look for other mechanisms, for example on the vascular system, before going for this. This issue came up several decades ago when hospital ultrasound machines became widely available.”

Dr Martin Coath, Associate Lecturer at Plymouth University, said:

“The first thing to clear about is that this work is pretty uncontentious. The author is simply calling for a detailed re-examination of a load of outdated guidelines and the revisiting of decades of results that suggest there might be a problem but have not been pursued with sufficient vigour or rigour. At this level the study reads – and this is not a bad thing – like a grant application.

“The measurement of noise levels, and the assessment of the effects they have on human health, are both inexact sciences. Noise that has always been almost impossible to perceive and much more difficult to measure has been widely ignored. The author’s point is that it is high time that the examination of ultrasonic ‘pollution’ achieved a level of inexactitude comparable with other types of noise.

“Ultrasound is a silent companion to everything we do. We make it when we rub our hands together or when we wrap food in aluminium 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.”

Dr David McGonigle, Research Fellow at Cardiff University, said:

“The title of this study may make one rather alarmed – ‘Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?’ – but it is less concerned with presenting new data on the topic than offering a ‘state of the nation’ summary of the field.

“Scientific papers take a number of forms: some focus on reporting the results of experiments that the authors themselves have performed, whilst others, like this study by Professor Leighton, seek to summarise and review work across a broad range of sources and disciplines. While its title may suggest otherwise, the paper actually does not present evidence to link mass ultrasound exposure to subjective symptoms like headaches or vertigo in the public. This is because – and it is a point acknowledged by the author – that there has yet to be a double blinded, controlled trial of such an exposure, which would ensure that people’s reporting of symptoms is not biased by their knowledge that they are currently being exposed to ultrasound.

“This kind of study is required because subjective reports of people’s symptoms are rarely accurate or well controlled – as is often stated ‘the plural of anecdote is not data’ – but the paper does demonstrate that industry standards may need updating, and larger sample sizes are required to ascertain if a link between exposure and symptoms does exist.”

‘Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?’ by T. G. Leighton published in Proceedings Of The Royal Society A on Wednesday 20 January 2016. 

Declared interests

None declared