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On Wednesday, the US embassy in Guangzhou, China, put out a health alert stating that a US government employee had experienced strange audio-related sensations. “A U.S. government employee in China recently reported subtle and vague, but abnormal, sensations of sound and pressure,” reads the report. The next day, a clinical evaluation of the employee revealed symptoms that match a mild traumatic brain injury. US Secretary of State Mike Pompeo said the symptoms were “very similar” and “entirely consistent” with the health issues that American diplomats in Cuba reported in August 2017. Those symptoms were blamed on “sonic attacks.”

But acoustics scientists don’t think there’s enough evidence to support the claims made in either Cuba or China.

“In the Cuban situation, there was a lot more hype than there was evidence … In Cuba, I don’t think the evidence was there for a sonic attack, and less so in China,” Timothy G. Leighton, Ph.D., a professor of ultrasonics and underwater acoustics at the University of Southampton tells Inverse. “I’m not saying it wasn’t; you’ve just got a heck of a long journey to take before you reach that conclusion.”

The diplomats’ symptoms could have other causes, and these other potential causes haven’t been eliminated, he says. Perhaps most significantly, the source of the so-called sonic attack has not been identified. The State Department has not reported finding a device to blame. Jinnie Lee, a spokesperson for the US embassy in Beijing, tells Inverse that the employee was examined and showed symptoms consistent with a minor traumatic brain injury.

“The Department is taking this incident very seriously and is working to determine the cause and impact of the incident,” she says.

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In September 2017, Inverse reported that acoustics researchers doubted the symptoms experienced by diplomats — hearing loss, speech problems, and mild traumatic brain injury — were caused by covert audio devices. When asked about the sonic weapons hypothesis, neuroscientist Seth Horowitz, Ph.D., responded bluntly.

Leighton is a little less certain than Horowitz, though he does argue that we don’t have enough evidence to say something else is definitely causing these health problems. Since 2015, Leighton has researched the effects of sound-producing devices on human health and found that there are lots of consumer devices on the market, especially in the US, that can expose people to dangerous sound levels. Any one of those products, in theory, could cause serious discomfort and stress, even if the device isn’t weaponized. Additionally, he points out, if someone was going to target diplomats, a sonic weapon would be particularly ill-suited, since middle-aged men have a much narrower range of audible sound frequencies than women and young people.

“The most robust people withstanding attacks seem to be middle-aged men, so if you’re targeting an embassy, it’s a peculiar weapon to choose for that,” says Leighton.

Beyond that, the source of people’s physical symptoms could be totally non-sonic, and he suggests that investigators have not sufficiently eliminated that possibility.

“The first thing to do is rule out every other possible cause: illness, stress, poisoning,” Leighton says. “Say we rule out every one of those, we’ve done due diligence. Then we go and record the sound, and you may think we have a slam dunk. But there are loads of other things in the world that can give people exposure to ultrasound: pest scarers, things that open doors automatically, public address systems.”

Even if diplomats are experiencing injuries and illness as a result of some sort of sonic device, the possibility of accidental exposure must be ruled out before this can be definitively called an “attack.” In a paper published in Proceedings of the Royal Society A in 2017, Leighton argued that a minority of regular people do indeed exhibit modest temporary adverse effects such as headaches because of their exposure to ultrasonic noise on a regular basis, effects which disappear shortly after the exposure does.

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Leighton says public address systems could produce significant discomfort in people without the need for some kind of covert sonic weapon.

In a paper published in JAMA in March of this year, the doctors at the University of Pennsylvania who examined the diplomats wrote that the patients’ symptoms do not paint a clear picture of what caused their issues. The affected individuals reported audible sounds in their residences, suggesting that the attacks were sonic and not ultrasonic, and they had issues with cognition and memory that persisted even after they were pulled out of Cuba, which doctors say is inconsistent with what we know about sound-induced injuries.

“Sound in the audible range (20 Hz-20,000 Hz) is not known to cause persistent injury to the central nervous system and therefore the described sounds may have been associated with another form of exposure,” they write. Leighton confirms this, saying that since the subjects were examined more than 200 days after their last exposures to the sound, he can’t support the idea that their symptoms came from ultrasound in the air. Furthermore, the doctors reported worrying signs, like losses in brain white matter, but there’s no way to know whether this was the result of pre-existing conditions.

Leighton points out that, weapon or no weapon, once the State Department announces that a tight-knit community is under attack, it only makes sense for its members to all notice and report symptoms, whether they had them before or not. Unpleasant sounds can cause stress, and in an already stressful environment, even annoying sounds could take on a sinister demeanor.

“If you play the sound of nails being scratched down a blackboard, some people will get stress headaches. We’re not talking about some kind of ultrasonic ray gun,” says Leighton. “If you ask a new parent near a crying baby, ask what symptoms they’re feeling. They’re experiencing a sonic attack.”

Editor’s note: As of 1:52 P.M. Eastern on May 25, 2018, this article has been updated to include a comment from the US embassy in Beijing and an additional comment from Timothy Leighton, Ph.D.