By Laurie Sullivan
The secret is out. Scientists have discovered what makes mozzies buzz off when they come across skin covered with a topical (rub-on) repellent containing the active ingredient, N,N-Diethyl-meta-toluamide.
(Yes, that’s a mouthful, which is why it’s better known as DEET.)
It seems that to mosquitoes, DEET makes people smell, well, awful.
DEET has been the gold standard in active ingredients – the part that does the actual repelling – in insect repellents for more than 60 years.
DEET-based formulas are used by millions of people every year since the 1950s. There have been very few reported cases of harmful effects from DEET or the other more recently approved active ingredients, such as Picaridin, IR3535, or oil of lemon eucalyptus, when they’re used as directed.
The DEET debate
News of the research into DEET came to us from Sydney University-based entomologist, Dr Cameron Webb, whose work and words we’ve featured in past Travelvax Report articles. The study was published in the Proceedings of the National Academy of Sciences this week.
“There’s been some debate about how DEET actually works,” Dr Webb said.
“We weren’t sure if it blocks the blood-feeding behaviour of mosquitoes or if it simply smells so bad that mosquitoes actively avoid it.
“Some researchers believed it confuses and disrupts the insect’s ability to detect odours given off by a prospective host.
“Others thought that DEET masks host odours, or that mosquitoes can smell DEET and actively avoid it and instead look for someone who’s not wearing repellent.”
The good oil in botanical repellents
To settle the debate, University of California researchers studied the response of the southern house mosquito (Culex quinquefasciatus) to DEET, non-DEET insect repellents, and a range of other chemical compounds.
They found that exposure to DEET activated an odour receptor in the mosquito’s antennae, sending it off to look for sweeter smelling skin. It’s a finding that could also make it possible to screen for new mosquito repellents.
The American researchers also looked to a potential new source of repellents, plants. Botanical extracts of plants, particularly essential oils, have been extensively studied as possible insect repellents.
While there have been many studies in recent times identifying new mosquito repellent candidates, getting people to use topical (rub-on) repellents as intended has been an even bigger challenge.
The search for spatial solutions
Indeed, Dr Webb says what we really need are more effective ‘spatial repellents’.
These are formulations released into the air from devices which protects a group of people (say, at a barbeque) and not just those who have applied repellent.
Some synthetic insecticides, such as metofluthrin, already hold this potential. However, understanding how mosquitoes detect and respond to new products may help scientists develop new mozzie-foiling strategies.
“It may be a while before these new repellents are on our supermarket shelves,” he said.
“In the meantime, my advice is to stick to what we know works – whether at home or while away on holidays.”
Our insect-avoiding tips
In reality, a holiday free of insect bites is difficult to achieve – especially in tropical or sub-tropical destinations. Mozzies can be relentless – especially if you miss a ‘deadline’ for reapplying repellent or miss an area of skin.
So, here are our tips for avoiding bites from mosquitoes and other insects:
Pack a repellent that really works: The higher the concentration of DEET, the longer the application lasts. Unless you plan on spending long periods exposed to mozzies, formulations that contain 40% (6 hours) will be fine. Products containing around 20%-30% protect for over 4 hours, while 10% formulations provide at least 2 hours of protection. Picaridin is equally effective as DEET and recommended by health authorities around the world. A 20% Picaridin-based formulation will protect for around 4 hours, while oil of eucalyptus-based formulations last for up to 6 hours.
For adult use only: Lower-dose repellents are suitable for children as young as 3 months of age. Many ‘low-dose’ DEET-based repellents have been replaced by picaridin-based ones in recent times. TWO IMPORTANT NOTES: (1) Don’t allow children to apply repellent themselves - it needs to be done thoroughly and correctly, and (2) If your child has a skin condition, check with your doctor before using any repellent.
Apply repellent to exposed skin only: A thin coating only of repellent should be applied to exposed skin, avoiding the eyes, mouth, wounds, or rashes. It’s a good idea to wash off repellent off kids when it’s no longer needed.
Seek and destroy: Mosquitoes don’t travel far, but they can breed in very small quantities of water lying around near your accommodation. On arrival, check for and get rid of containers that could be potential breeding sites on balconies and in gardens.
Avoid insect ‘rush hour’: Dawn, dusk and early evenings are peak feeding times for mozzies: The times when they’re most active. If coming indoors isn’t possible, make sure the repellent is working.
Dress up: Part of your strategy for avoiding insect bites should be dressing in lightweight long pants and long-sleeved shirts, plus shoes and socks, especially at peak times if you can’t get out of the firing line. This is particularly important for kids, who are an easy target for mozzies. Don’t forget to bring a light gauze netting to protect babies in strollers.
Other things we know about avoiding bites
Here are some facts on what DOES NOT WORK when it comes to avoiding insect bites.
- Wristbands simply don’t work.
- Phone apps don’t work.
- So-called ‘natural’ alternatives to the active ingredients mentioned earlier are unproven and may not be effective. Some plant-based repellents will need to be reapplied much more frequently than either DEET- or Picaridin-based products to provide protection.
- Taking vitamin B doesn’t prevent bites. In fact, there is no evidence that anything you can eat or drink will prevent bites.
- Burning mosquito coils and sticks may reduce the number of bites but they won’t stop them completely. Never burn these indoors overnight.
- Don’t use products that combine sunscreen and insect repellent. Apply sunscreen at least 20 minutes before going outdoors, then apply repellent just before exposure. Reapply both as needed.
And, before you fly…
Check on the latest mozzie disease risks at your destination country by calling Travelvax Australia’s travel health advisory service on 1300 360 164 (toll-free from landlines).
There is no obligation and you can also make an appointment for a pre-travel medical consultation at a Travelvax clinic to review your travel vaccines, obtain any immunisations or medications recommended, buy accessories, and get advice tailored to your itinerary and personal medical history.