Are electronic mosquito repellent devices as effective as their manufacturers' claim? A Consumer Council study cast doubt on the claimed effectiveness of electronic mosquito repellents and pest repellers.
The study covered 19 electronic mosquito repellent devices and pest repellers available on the market. It probed into the claims made by the manufacturers of these devices that they can repel effectively biting mosquitoes or pest. The study revealed that their efficacy was questionable.
14 models of electronic mosquito repellent devices, with prices ranging from HK$79 to HK$290, and 5 models of pest repellers, which are more expensive on average, with prices ranging from HK$198 to HK$498 are included in the study. The devices claim to operate with sonic, ultrasonic and electromagnetic waves.
Among the examined models, 2 used the word 'ultrasonic' in their product names, and 2 in the packaging. According to UNEP, WHO and IRPA, ultrasound generally refers to a sound wave with a frequency above 16,000Hz. However, the Council found that the frequency range of emitted sound wave claimed by those devices (ranged from 6,000Hz to 12,000Hz) did not fall within the above-mentioned range of ultrasound.
Some of the 'sonic' mosquito repellents claimed they would emit sound waves of frequencies in the range of 5,000Hz to 9,000Hz, mimicking the wing flapping frequencies of male mosquitoes, and would frighten away the blood sucking female mosquitoes. However, there is no scientific evidence to support the efficacy of sound waves in repelling mosquitoes.
It is also not evident that ultrasound can effectively repel mosquitoes and insects. Even if it can, the strength of the ultrasound emitted by the ultrasonic devices is very likely to be weakened at places inside the house where the ultrasound is blocked/absorbed by walls and furniture.
According to the Food and Environmental Hygiene Department, over 70 species of mosquitoes have been identified in Hong Kong. Though some of the devices claim to provide different modes of operation which repel different species of mosquitoes or pest, they could be operated on only one mode at any one time, meaning that even if the product is effective, it is unlikely they can repel various species of mosquitoes at the same time as claimed.
The label on a few devices indicated that the products had obtained a certificate or registration number issued by the US Environmental Protection Agency. However, neither do the numbers reflect the product's safety and performance levels, nor do they certify that the product is endorsed or guaranteed by the Agency.
The efficacy of electronic mosquito repelling devices has long been an issue of concern. Many overseas authorities/organisations have cast doubts upon the effectiveness of the electronic repellents. The US Centers for Disease Control and Prevention and American Mosquito Control Association have both pointed out that ultrasound repellers cannot effectively prevent mosquito bites or repel mosquitoes. The Cochrane Infectious Diseases Group also concluded electronic mosquito repellents did not help in preventing the spread of malaria. There have been legal actions in Australia and the US against suppliers of electronic repellers for alleged deceptive and misleading claims.
Some electromagnetic pest repellers claim to be able to ward off spiders, cockroaches and mice. But the US Environmental Protection Agency questioned the effectiveness of electromagnetic devices in controlling pests years ago and expected these products to be removed from the US market.
Consumers relying on the efficacy in repelling mosquitoes claimed by electronic mosquito repellents might neglect taking other measures to prevent mosquito bites. The most effective mosquito prevention measure starts from the source by tidying up the household environment to eliminate the potential breeding places for mosquitoes.
The July issue of CHOICE magazine (no.429) offers the following tips for preventing mosquito bites:
For indoor environment:
- Install mosquito nets or screens to prevent mosquitoes from flying indoors.
- Use conventional mosquito coils, electric mosquito mats, electric liquid repeller and spray which contain pyrethroids that are effective in driving away mosquitoes.
- When using insecticide spray, food should be moved away. Kitchen utensils, toys, fish tanks and pets should also be removed, people should leave the room. Since the spray often contain flammable compressed gases, they must not be sprayed near flame and the can should be stored properly.
For outdoor activities:
- When you are outdoors, wear long-sleeved and light coloured clothing, attach a mosquito patch on clothes. Apply suitable mosquito repellents (e.g. DEET-based repellents) onto exposed parts of the body.
- Avoid going for an outing at dawn and sunset.
- Install mosquito traps.
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