miracle solution or sham?

There are all kinds of unlikely things on YouTube. While looking for a miracle cure for mosquitoes, maybe you came across ultrasound videos promising to protect you from these pests? Some of these videos have been viewed hundreds of thousands of times, sometimes even more than a million. They are several hours long and end-to-end, they can be played in "playlist" mode and can last up to seven days without requiring any action on your part. A week of respite against mosquitoes without having anything to do, what to ask for more?

On these videos, the interest is obviously not the image but the sound. What do we hear? Nothing. This may seem logical since ultrasound, these sound waves whose frequency exceeds 20 kHz, are generally inaudible to the human ear. On some videos, however, we hear a shrill and continuous sound. A "beep" particularly unpleasant to listen that makes you want to stop everything.

Unfortunately, the effectiveness of these videos seems close to zero, as suggested by the many comments posted on the YouTube page. Questioned by Franceinfo, acoustic specialists do not give them any credit. First, these videos undergo compression that can alter the ultrasound when uploaded to YouTube. Then, your computer speakers or the speaker of your smartphone are unable to play any ultrasound.

"Even good quality speakers will not broadcast ultrasound properly, most are made to human auditory sensitivity, that is to say from 20 Hz to 20 KHz ", explains Thierry Aubin, bioacoustician and research director at CNRS. These videos, most often posted by non-specialists, have not been the subject of any serious study.

Mobile applications available on the AppStore or Google Play, which say emit ultrasound to scare away mosquitoes, so are also likely to be completely useless, as shown by this test made and filmed by a user.

Several scientific works have instead been interested in small ultrasonic boxes and whose manufacturers promise that they drive away mosquitoes. "All publications are unanimous: these ultrasound systems have not been scientifically proven", tells franceinfo Frédéric Darriet, medical entomologist at the Institute for Research for Development and author of Mosquitoes and humans, Chronicle of an announced outbreak

The researcher refers us to a study published in 2010 in The Cochrane Library, which screened 10 studies conducted in North America and Africa to judge the effectiveness of these cases. The result is clear: none of these studies showed a reaction of mosquitoes to the presence of ultrasound, whatever the frequencies tested.

There is therefore unfortunately no miracle method to protect themselves against the mosquitoes that come to invade us on the terraces or in our bedroom. Indoors, the best way to prevent mosquitoes, "it's the good old mosquito net, possibly impregnated with a repellent product", observes Frédéric Darriet, or the installation of a sufficiently fine fence on the windows of his home

Another proven method: the repellent (based on Deet, KBR or IR3535) sprayed on skin and clothing. But these products only work for a short time: six hours on average under normal conditions, less if you sweat or dive, for example. And they are to be used with moderation, especially in children and pregnant women, because the chemical applied on the skin can potentially end up in the body.

As for the often touted natural repellent methods, such as lemongrass, they have not proven effective. "No studies have shown that lemongrass has any effect on mosquitoes, says Frederic Darriet. Heaps of companies sell candles or bracelets scented with lemongrass, but it's the powder in the eyes, it is useless. "