Public health fears for ultrasound
Ultrasound is any noise with a pitch higher than 20 kiloHertz - that's 20,000 waves per second. These sounds are beyond the normal hearing range of humans, but despite being silent, exposure to it has been linked to symptoms such as nausea, headaches and fatigue in a small percentage of people. And now a review published this week is calling for measures to limit people's exposure to the sounds. According to the report, current safety guidelines are outdated, inappropriate and based on poor statistics. After receiving several letters from people claiming ultrasound was affecting them, the review's author, Southampton University's Timothy Leighton, decided to do some detective work, as he explained to Georgia Mills...
Timothy - First of all, I went out with a little team of volunteers and we looked to see what ultrasound was out there and, to be honest, we were quite astounded because there are the devices that produce moderate levels of ultrasound, like some of these automatic door opening systems, which open when someone breaks the ultrasonic beam as they walk towards them and some which produce quite intense ones. One, for example, was coming from the loudspeakers in the public address system in a rail station, which has a footfall of 3 million people, and there we found the reason for this is because, under EU legislation, the operators of these loudspeakers have to, at all times, know that they're working in case they need to evacuate the building, saying 'fire alert, fire alert' or whatever. To do that, they can't obviously say, testing, testing, one, two three all the time - that would annoy people - so, they send an ultrasonic signal between these loudspeakers in the belief that no-one can hear it and no-one will be perturbed, but these people were being perturbed. So I said to myself, okay, I'm going to try and look at the guidelines that protect these people and, you know, there must be levels that control what we put out, and found problems in those guidelines.
Georgia - What problems would you say these guidelines had?
Timothy - There's a lot of guidelines - a dozen or more - and they all seem to agree, roughly but when I looked into it they weren't agreeing, they were copying each other. Each time a new country, or an organisation needed new guidelines, it just saw what was out there and copied it and that gave the impression of consensus. And if you actually traced it back to the original evidence these guidelines were based on, you found a number of worrying things. They were based really on about six studies in the 1960s and 70s and they were primarily looking at the scenario where a man would be operating an ultrasonic cleaning bath at work, and the guidelines would be based on a man in the occupational setting who could then put on earphones, or be moved to another job, or be protected in some way from the source because he knows he's been exposed. And I say man because these studies were, primarily, using tests on adult males. Now we know that people lose their sensitivity to high frequencies as they get older and, in fact, many of these males worked in industry or had worked in the services and had operated firearms so, really, they were a bad set of people to test in order to produce guidelines to protect the public. You might have a grandmother who can't hear a high frequency holding in her arms a baby who can, not knowing why this child is perturbed. It's unreasonable to think they would wear hearing protection to protect themselves; we don't know how many hours per day they would be exposed and so the guidelines seem to be based on poor statistics, and wholly inappropriate for protecting the public to the kind of exposures we see them being exposed to today.
Georgia - But if ultrasound is, for the most part, beyond human hearing, how could it be causing symptoms of nausea, fatigue, and headaches? Well, Tim has a rather neat theory; when you're exposed to ultrasound your eardrum vibrates but the signal is not converted into a sound. However, other receptors do send your brain the message that, indeed, your eardrum is moving and this discrepancy between signals could confuse your brain, much in the same way as seasickness does.
Timothy - And what symptoms do we get from seasickness: headache, nausea, dizziness, fatigue - exactly the same set of symptoms. So, I'm not saying that ultrasound is causing seasickness; I think it's way to early days to look at that but I would like to put that on the table as something knock down so that we can get off the ground some sort of attitude to people who come claiming to have ill-effects from ultrasound that doesn't immediately dismiss them.
Georgia - If you fancy trying your hat at some detective work, Tim has released an app for smartphones, which can detect ultrasound, and it turns out it might be used in some unexpected places.
Timothy - There are strange and bizarre claims by companies of things that they will do with ultrasound. There was a company in the States that said it was developing a system whereby instead of plugging your mobile phone into the wall to charge it, you just hold it up in the air and it will beam ultrasound at it to charge it. There is even companies that claim to embed into adverts and websites, a code - a beep, beep, beep - at ultrasonic levels so, if you think you're in an anonymous environment like a hotel or an internet cafe, what they claim to be able to do for a fee is to embed an ultrasonic code into the adverts and your phone picks that up - a beep, beep, beep - without you knowing. Your phone has software on it you don't know about that identifies you and the thing you're watching, and then sends a signal back to inform the company of what you were doing. That's another area in which we, as people, are expanding into using ultrasound without the public knowing and, if we're exposing the public to such radiations, we need to get our public health framework accurate for that.