Hong Kong’s sub-tropical climate is perfect for outdoor fun. We have the ideal weather for hiking, beaches, outdoor brunches—and, unfortunately, mosquitoes.
Mosquitoes buzz all-year round here but appear in abundance from April through until about October.
When it comes to preventing bites, if you’re someone who has tried everything in vain, we feel your itch!
Here we look to science to better understand which repellents work and find relief for our families.
The most common active ingredient in insect repellents is DEET (or N,N-Diethyl-meta-toluamide).
It’s so widely used because there are few other chemicals which come close to its efficacy against both mosquitoes and midges.
It is considered safe by scientists and doctors, along with bodies like the World Health Organization, who particularly recommend it for regions where people are at risk of serious insect-borne diseases.
Did You Know?
Mosquitoes use a receptor to detect carbon dioxide, so those who exhale more CO2 (if you’re larger or taller) are more prone to bites.
People with blood type O or who are pregnant also get bitten more, research shows.
The Problem With DEET
Many people are concerned about the use of DEET, as it’s a chemical that’s absorbed through your skin. It is known to irritate the eyes and has a distinct, often unappealing, odor.
It’s also a plasticizer that has been known to cause damage to items such as synthetic clothing, backpacks, glasses, watches and cameras.
In intense doses—and in very rare cases (around 1 per 100 million people)—it has been reported to impair the nervous system with symptoms including seizures, tremors and slurred speech.
But if used as directed, DEET has been found to pose no health risks. So always make sure to read the application advice on the product, particularly for children.
Is DEET safe in pregnancy?
There’s been no evidence that it’s harmful to the fetus. Although the chemical was found to cross the placenta line in 8% of women who used it regularly in the second and third trimesters, there were no adverse effects on survival, growth or development of their babies—at birth or at one year, Thailand’s Faculty of Tropical Medicine found.
If you want to err on the side of caution and avoid it altogether, there are some potentially healthier alternatives.
The Alternatives to DEET
The Environmental Working Group, EWG, spent 18 months investigating the safety and effectiveness of chemical repellents in 2013.
Although it concluded DEET to be a ‘reasonable choice’ when weighed against the consequences of mosquito borne diseases, it recognized other options.
Here are three alternatives highlighted by its environmental researchers:
1. IR3535 has been used widely in Europe for over 20 years, with no reports of health problems. It can be very irritating to the eyes, and, like DEET, can damage plastics, but at 10-30% strength it has a good record of repelling the Aedes mosquito, and ticks.
TIP: Avoid sunscreens that contain IR3535 as reapplication every two hours would over-expose you to the repellent.
2. Picardidin performs well in tests—although it’s not as widely tested—and has none of the disadvantages of skin irritation, odor or damage to plastics. It also evaporates from the skin more slowly than its counterparts, so may repel bugs for longer periods.
TIP: At 20% concentration, it will be effective against mosquitoes and ticks for 8 to 14 hours.
3. Oil of Lemon Eucalyptus/PMD is a repellent based on the extract of the eucalyptus tree that has been refined to intensify the concentration of the naturally occurring substance PMD.
It can be an effective choice for some situations but is not recommended in areas with a high risk of West Nile virus, sand flies or biting midges.
TIP: As a biochemical pesticide, refined oil of lemon eucalyptus undergoes fewer safety tests than synthetic chemical alternatives. Always be sure to read the manufacturer’s label, especially for use on children.
Can We Banish the Chemicals?
If you’re looking for a completely chemical-free repellent, we’re going to be the bearers of bad news!
Eating garlic, taking vitamin B supplements, and even burning citronella candles are all widespread myths that have been debunked by numerous studies.
In 2017 the Journal of Insect Science published an in-depth report into a range of mosquito devices: from sprays and sonic repellers to clip-on devices and candles.
Researchers tested their efficacy against the Aedes aegypti (the Zika mosquito) and found the sprays containing DEET or Oil of Lemon Eucalyptus came out top, as well as a clip-on device containing the pesticide metofluthrin.
Neither the various essential-oil based devices or the citronella candle made any difference to mosquito behavior.
The only effective chemical-free alternative is to make repellents your last choice and follow some simple pointers to fend off mosquitoes:
- Avoid grassy areas and stagnant water.
- Don't use heavily scented soaps and perfumes.
- Wear hats, long sleeves and long pants (yes, we know this is hard in the summer!)
- Tuck your pant legs into socks or shoes.
- Stay indoors during peak biting times at dawn and dusk.
- Use window screens or bed netting indoors.
- Turn on the air—mosquitoes feed less when there is a moderate breeze.
- Skip the lager. Studies show that malaria mosquitoes prefer beer drinkers!
At the end of the day, there’s no way to completely avoid mosquito bites if you love the outdoors life.
If you’re traveling to high-risk disease areas you may prefer a stronger chemical, but you could decide these aren’t warranted for your winter hike in Hong Kong, for example.
Armed with this knowledge, hopefully you and your family can stay healthy and itch-free during mosquito season!