Mosquitoes aren’t just annoying. Every year around 5,000 Australians get sick following a mosquito bite. Most commonly the infection is Ross River virus but there is annual activity of dengue viruses in north Queensland and there are occasional cases of the rare, but potentially fatal, Murray Valley encephalitis virus.
Spraying insecticides may kill some mosquitoes around our backyards but it won’t completely protect us from mozzie bites.
Tipping out, throwing away or covering up any water-holding containers around the backyard will take away opportunities for them to breed in our backyards. But there isn’t much you can do if they’re flying in from nearby wetlands.
Mosquitoes aren’t going anywhere. They’re a natural part of our environment and they’re increasingly finding a home within our cities. We’re going to have to learn to live with them, and take on the challenge to avoid their bites.
The first line of defence
Avoiding wetlands or bushland at dawn and dusk will ensure you’re missing the time and place where mosquitoes are most active.
Wearing light-coloured long-sleeved shirts and pants won’t repel mosquitoes but you’ll attract fewer to you. Those that do land will be less likely to bite through if clothing is loose-fitting. You can also consider treating the clothing with insecticide for added protection.
For exposed skin, there really isn’t an alternative to topical insect repellents. There is nothing you can eat or drink that will prevent mosquito bites so you’ll need to pick out your favourite repellent formulation.
Any product for sale in Australia purporting to repel mosquitoes must be registered with the Australian Pesticides and Veterinary Medicines Authority. The label on your repellent will tell you what the ingredients are in each formulation. But not all repellents are equal.
The most effective topical repellents are those that contain either DEET or picaridin. These two products have repeatedly been shown to protect against bites and, despite the common misconception, have shown to be safe to use, including on children over the age of three months.
While there is still some debate about whether products such as DEET and picaridin actively repel or simply confuse mosquitoes looking for blood, there is no doubt that when applied to exposed skin, they stop biting by mosquitoes.
It is, however, important to understand what the “strength” of a formulation tells you about how well it will repel mosquitoes.
Let’s take DEET as an example. The “strength” of the repellent (the concentration of DEET in the commercial formulation) will determine for how long mozzies are prevented from biting. This means that for short periods, say around two hours, a “low dose” repellent will stop just as many mosquitoes from biting as a “high dose” (often called tropical strength) repellent.
But while that “low dose” repellent may stop working after a few hours, the “high dose” repellent will provide protection for many, many hours. The same equation applies to picaridin-based repellents.
In Australia, the highest-dose repellent contains 80% DEET and laboratory studies have demonstrated over ten hours protection from biting mosquitoes.
But if you’re only going to be outside for a short period, there is really no need to use a “high dose” formulation.
Extracts from many different plants have been purported to repel mosquitoes. In many cultures, smouldering aromatic leaves have been used to repel mosquitoes with some success. But what about plant-based topical repellents?
Some of the most widely available “botanical” repellents contain one or a blend of citronella, tea-tree, eucalyptus, lavender or catmint oils. Essential oils from Australian native plants are also popular.
But rarely do these repellents provide the same duration of protection as DEET or picaridin-based repellents.
If you’re only outside for a short time, this may not be a problem. If you’re heading out for a bush walk, picnic near local wetlands or a stint of gardening in the late afternoon, you’ll need to reapply “botanical” formulations three to four times as frequently as low dose DEET-based repellents.
It’s also important to remember that although these “botanical” repellents are often perceived to be safer to use, there are plenty of examples of adverse skin reactions resulting from the over application of essential oils to skin.
Even registered botanical products are generally not advised for use on children under 12 months of age.
There are plenty of mosquito coils and sticks available that contain plant-based repellents such as citronella. While these help reduce the number of biting mosquitoes, they won’t provide the complete protection that a topical DEET-based repellent will.
It’s not just what you choose but how you use
It doesn’t matter what type of repellent you choose, unless there is a complete application to all exposed skin, you won’t be completely protected. Mosquitoes are highly skilled at finding the smallest chinks in your repellent armour.
Spraying repellent on clothes or giving a dab “here and there” won’t provide protection. You need to apply it like you would sunscreen but probably not quite so much. A thin cover is enough for short periods of protection.
Obviously, reapplication is required after swimming or sweating.
What about those wrist bands?
In the middle of a hot and humid summer afternoon, rubbing a somewhat sticky substance over your skin is far from appealing. It’s little wonder that there is great interest in wrist bands and patches that purport to protect against mosquito bites.
But they only work for a few millimetres either side of the band. Laboratory testing of wrist bands containing an essential oil indicated that while there was a reduction in the number of mosquitoes attempting to bite close to the band, there was little protection on the upper arm. They don’t provide “whole body” protection against biting mosquitoes and aren’t an effective alternative to topical repellents.
Botanical products and wristbands are marketed as “safer”, “more natural” or “more convenient to use”. But users may be inadvertently putting themselves at risk of mosquito-borne disease. DEET- or picaridin-based repellent formulations provide the best protection.
About The Author
Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney