Insect repellents work by either blocking the cues that identify the wearer as a potential blood meal or providing an odour that overrides that of the your natural scent. There are a wide range
of repellents available, broadly categorized as either synthetic or botanical in nature.
The most effective and widely used repellent internationally is DEET (diethyltoluamide). Developed by the United States Army in the 1950s, DEET is now used by many millions
of people around the world and is available in a wide range of application formulations (e.g. roll-ons, lotions, aerosols, pump-sprays and wipes) and concentrations.
Generally, repellents containing less than 10% DEET will offer up to two hours’ protection from mosquitoes. Repellents that contain up to 80% DEET are more suitable for long periods of exposure to mosquitoes in areas of endemic vector-borne disease.
Picaridin is another widely available active ingredient found in commercial insect repellents in Australia. This product was developed more recently, is generally thought to have a more pleasant scent than DEET and has lower toxicity to humans (making it more appropriate for use on children). Scientific studies have shown that this product is equally effective at
preventing insect bites as DEET.
There are a large number of plants whose essential oils or extracts may provide protection against biting insects. The most common products come from strongly aromatic plants, such as eucalyptus or teatree, and commercial products often contain a blend of extracts. Many scientific studies have compared botanical and synthetic repellents and, although botanical products may provide some protection, products such as DEET and picaridin provide substantially greater and longer term protection, even at low concentrations. Some natural products offer protection for only a few minutes, leaving users unprotected and exposed to disease-carrying vectors.
However, research on repellents with botanical-based active ingredients is continuing and these products may be useful under some circumstances.
Coils, sticks and other gadgets
Burning plant material to repel biting insects has been used by many cultures for thousands of years. Today, the tradition continues in the form of mosquito coils and sticks. The mosquito coil is the most popular form of personal protection from biting insects over the past 100 years. These devices are made of materials impregnated with insecticide (e.g. synthetic pyrethroids, such as allethrin) that burn slowly (some coils burn for up to eight hours) and may provide up to 80% protection. Some formulations are also available with botanical active ingredients, but these
are generally less effective. Coils are cheap to produce and easy to operate, although the smoke produced may present a health risk when used indoors. There is also a number of electronic units available (for both indoor and outdoor use) that release insecticides from slow-release mats or liquids. These units can be very effective, as the pyrethroids kill mosquitoes rather than
simply repelling them.
A wide range of products claim to repel biting insects in formulations other than topical repellents. Products containing synthetic or botanical active ingredients can include patches and wrist bands that claim to provide a degree of protection. However, scientific studies have shown that these products offer substantially less protection than topical repellents.
All repellents used in Australia, whether synthetic or botanical, must by law be registered with the APVMA and the approval number must be listed on the label. There is often a perception that synthetic repellents, such as DEET, are unsafe. However, despite the widespread use of DEET-based products internationally, there are very few cases of adverse reactions. Most of these cases involve serious misuse, most commonly applying too much of the product (especially on young children), eating it or exposing the eyes to the product. Botanical-based products can
also cause irritation. The risk of an adverse reaction from using a repellent is very low and failing to use repellents in some locations will almost certainly result in insect bites and the real possibility of acquiring an infectious disease. Regardless of the active ingredient, all repellents should be applied according to the instructions on the label.