Summertime means hammocks, BBQs, fireworks, and mosquito bites.
At least it does for me. Those rotten little suckers seem to just love me. They鈥檒l flock to me even when there are three other people sitting in my backyard. What is it about my blood that they seem to enjoy so much?!
Let鈥檚 take a look at the science behind mosquitos and try to answer two questions: Why do mosquitos bite certain people, and what should we do to make them stop?
Take-home message:
-听Blood type may or may not play a role in attracting mosquitos
- Products using DEET, icaridin, PMD, metofluthrin, and some blends of essential oils are effective at repelling mosquitos
-听Bug zappers, sonic devices, citrosa plants, B vitamins, and scent-baited traps are not effective at repelling mosquitos and should be avoided
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Mosquito isn鈥檛 a Species, it鈥檚 a Group
Before discussing the nitty-gritty of mosquito attraction, we need to realize something. While we tend to think of all flying bugs with proboscises as mosquitos, in truth there are more than 听categorized into 112 genera that fall under the moniker of mosquito.
With such variation in species comes a lot of 听in habitats, behaviours, and risks. For instance, malaria is transmitted to humans only by mosquitos of the genus Anopheles, while yellow and dengue fever are transmitted by those in the genus Aedes. Canada is home to roughly听听of mosquitos belonging to the genera Anopheles, Culex, Aedes, Mansonia,听and听Culiseta. Some mosquitos are anthropophilic, meaning that they preferentially feed on humans, while others are zoophilic and preferentially feed on animals.
We鈥檙e typically taught to remove standing water from our property and avoid boggy or marshy areas (good luck ) to avoid mosquitos, but some species of these bugs don鈥檛 exclusively lay their eggs in water. We tend to think of mosquitos being at their worst in the summer, at dusk and dawn, but different species are active at different times, and their behaviour can even change from season to season, making it hard to predict when we are at risk of getting bitten.
Something that is true of all mosquito species though is that only the females bite. They require a blood meal in order to produce their eggs. The nasty by-product of this reproductive cycle is that they transmit diseases, and actually 听per year than any other animal.
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How Mosquitos Track You
Mosquitos home in on their dinner-to-be by following a few different signals. The听first clue that something biteable is nearby is the of a CO2听plume exhaled on the breath of mammals and birds alike.
The amount of CO2, however, does not affect the attractiveness of a specific target, so even if you鈥檙e a human who produces more CO2听than others (such as those who are larger or ) that alone is not responsible for your irresistible-to-mosquitos aura. This makes sense since large animals like cows naturally produce much more CO2听than humans, yet many mosquito species still prefer to bite us.
Mosquitos will track a CO颅2听plume until they encounter . These first of these clues that a target is close by is usually smells emanating from the skin, which we鈥檒l discuss more in a second. As they get close听to the source of a smell, mosquitos will then detect and head towards heat and moisture signals emanating from a body.
We don鈥檛 know whether affect how attractive you are to a mosquito, but we do know that increases the volatile compounds on your skin that they love, and that anhidrotic people, or those who show decreased sweating, are to the pests.
The main mosquito-cues that can differ between humans are the olfactory ones. While it鈥檚 easy to swap your shampoo and soap for unscented varieties that won鈥檛 attract mosquitos like the do, a lot of the smells that mosquitos sense are innate to your physiology and sadly are not something that we can really change.
A few of these odorous chemicals include ,听,听, and . For many of these compounds, however, higher concentrations don鈥檛 equal greater mosquito attraction. Instead, they modulate the attractiveness of other substances. For instance, lactic acid has been shown to increase mosquitos attraction to 听and .
While an animal may produce similar-to-human levels of CO2, humans tend to produce than primates or cows. This lactic acid increases the appeal of CO2for anthropophilic mosquito species, while zoophilic species from landing on you. Conversely, ruminants like cows also exhale, a substance that attracts zoophilic species of mosquitos. In a demonstration of this, skin rubbings taken from cows were to anthropophilic mosquitos as skin rubbings from humans via the addition of lactic acid.
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The Role of Blood Type
There has been significant debate over the role blood type plays in attracting mosquitos. Initially, using 锘�Anopheles gambiae听found that mosquitos preferred those with O type blood (O>B>A>AB). But 听study using the same mosquito species did not confirm this.
A examined 736 patients and found that while those with A type blood made up 17.6% of the control group, they made up 29% of the malaria cases. Conversely, those with type O blood made up 33% of the control group but only 22% of the malaria cases. While this alone does not tell us whether or not certain blood types are more likely to be bitten by mosquitos or contract malaria, it does point to blood type playing some role in mosquito attraction.
Some clarity came with 听study done with 锘�Aedes albopictus that found a similar pattern to the original 1972 study: O>B>AB>A. The researchers also compared the mosquito-attracting ability of those who secrete substances corresponding to their blood type onto their skin, versus those who do not. Their theory was that these blood type-specific secretions could explain mosquito鈥檚 ability to find their preferred type O prey. Their results, however, showed an order of preference of O secretors>A nonsecretors>B secretors>O nonsecretors>A secretors>AB secretors>B nonsecretors, which do not correspond to the blood type preferences established.
Concerning blood type鈥檚 role in attracting mosquitos, we鈥檙e stuck with the often-written phrase more research needed. Given the conflicting results and relatively small sample sizes of these studies, we cannot make definitive conclusions. Not to mention that we have no idea how mosquitos are able to detect a target鈥檚 blood type from a distance.
If mosquitos do truly target those with type O blood, the authors of theorize that preference could have evolved due to the prevalence of type O blood in African nations. The three African nations are Nigeria, Ethiopia, and Egypt, and the percentage of their populations with type O blood 听51.3%, 39.0%, and 52.0% respectively.
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How to Avoid Getting Bitten
Anyways, even if we knew what blood types attract mosquitos, you can鈥檛 change your blood type. So, what can you do to get some relief from these minuscule menaces?
First, it鈥檚 important to remember that just because you鈥檙e not forming welts doesn鈥檛 mean you鈥檙e not getting bit. Not all bites will lead to the familiar welts, so even if you鈥檙e not covered in itchy bumps, if you鈥檙e near mosquitos you should be using repellant.
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Things That Work
Physical barriers should be your听against mosquito bites. Install screens on your windows, doors, tents, and RVs, and cover children鈥檚 cribs, playpens, and strollers with fine mesh to keep mosquitos out.
You can get specialty meshes and clothing treated with , an insecticide, for adults in Canada. The anti-mosquito effects of the chemical will last through several wash cycles, but permethrin-treated objects should never be used for or around children, including听screens or mosquito nets that they may interact with, as their safety .
In general, you should strive to wear light coloured clothing, and cover as much of your skin as the heat will allow. Mosquitos are better able to towards darker targets, so skip the Nirvana t-shirt and try on a white tee instead.
Flowery and fruity scents will attract mosquitos greatly since they 听(in addition to us) but even non-botanical scented products should be avoided whenever possible. This includes (amongst many others): shampoo, soap, conditioner, shaving cream, aftershave, perfume, deodorant, hand cream, makeup, and even laundry soap and softener.
In terms of repellants, the good news is that you have more options on the market than ever. The bad news is that only some of them work.
DEET
N,N-Diethyl-meta-toluamide, better known as , has been the standard ingredient in commercial bug sprays since 1957 when it made the jump from military to civilian applications. While it used to be thought that DEET interfered with a mosquito鈥檚 ability to detect lactic acid, more has found that mosquitos detect and avoid DEET directly. Much like I do with vinegar.
Misguided fears about DEET鈥檚 safety have spurred some to move towards other mosquito repellants, and while there are other effectual repellants, none work as well or for as long as DEET. In terms of its safety, DEET has been than any other repellant and when used according to guidelines is quite safe.
When utilizing DEET-based repellants it鈥檚 important to pay attention to the concentration of DEET in the product. The that no concentration over 30% be used on anyone and that only formulations containing up to 10% be used on children aged two to twelve (up to three daily applications) and aged 6 months to 2 years (only one daily application). Babies under 6 months should be kept mosquito-bite free through the use of nets and screens rather than repellants of any type.
Icaridin
, also known as picaridin, is a safe alternative to DEET and by the Government of Canada for use against mosquitos and ticks on anyone over the age of 6 months. showed that products with 9.3% icaridin can repel mosquitos for up to 3 hours, while showed that a 10% concentration repelled mosquitos for more than 7 hours. This is comparable to the 听to 听hours of protection provided by 7-15% DEET products, although DEET has been more widely studied. Contrarily found a 10% icaridin repellant rather ineffective. If you find them effective, icaridin-based products could be particularly useful for small children who have exceeded their daily recommended applications of DEET-based products but still need to remain outside.
Citronella
Citronella has long been the standard of backyard BBQs and picnics in its candle form, but in addition to the coils and candles designed to keep mosquitos out of a particular area, there are also repellants that contain citronella oil.
Citronella oil is made mostly from 2 species: C. nardusand C. winterianus, and contains , the most notable in terms of their insect-repelling nature include camphor, eucalyptol, eugenol, , and .
While it鈥檚 citronellal that provides the flowers with their characteristic lemony scent, 鈥檚 findings suggest that it is actually linalool and geraniol that provide the bug-repelling effects. The researchers compared candles made of 5% citronella, linalool, and geraniol, and found the geraniol and linalool candles much more successful at repelling mosquitos than normal citronella (85% and 71% versus 29% repellency rates over 3 hours). likewise confirmed straight citronella candle鈥檚 inability to effectively repel mosquitos alone.
examined three mosquito repellants that contained citronella and found them all significantly less effective than formulas containing DEET or icaridin, and examined 3 wearable bracelets that claimed to emit geraniol and found them as effective as using no repellant at all.
So while it could be useful to burn a geraniol or linalool candle while you鈥檙e sitting outside, you should probably still backup your protection with an effective repellent.
P-Menthane-3,8-diol (PMD)
Products with , a chemical found in small amounts in oil extracted from the , have generally (studies ,,) show it to be as effective as DEET and icaridin. The Canadian government 听PMD鈥檚 repellency effects on blackflies and mosquitos but recommends against using PMD-containing products on anyone younger than three.
Soybean and Essential Oils
Soybean oil is perhaps the strangest bug-repelling ingredient on this list, but repellant formulations containing mixes of soybean oil and various essential oils have been rapidly making their way onto the Canadian market. While the soybean oil itself does not repel mosquitos, it works in tandem with the essential oils also included in the repellants to stabilize their volatility.
found that a formulation including soybean oil, coconut oil, geranium, and vanillin repelled mosquitos for more than 7.2 hours. However, the same study, , showed that other formulations also containing soybean oil, as well as other various essential oils (menthol, eucalyptus, lavender, rosemary, sage, etc.) worked very minimally.
This points to the particular essential oils and other ingredients in the repellant making the difference rather than the soybean oil itself. This makes sense when you consider that the geranium included in the effective soybean repellant was likely citronella, and that vanillin has been to increase the repellency effects of citronella.
The Government of Canada doesn鈥檛听听any age restrictions on formulas containing soybean oil but recommends not using essential oil formulations on those younger than 2. So, you鈥檙e free to experiment with different products using different ingredient blends and see which works, but make sure to turn to something a bit more reliable when actually venturing into the woods.
Metofluthrin
If you鈥檇 rather wear a clip-on device than use a mosquito repelling lotion or spray, your only good option is those that emit metofluthrin. This examined the efficacy of 5 wearable anti-mosquito devices and found that only the metofluthrin at a concentration of 31.2% effectively repelled mosquitos. Much like citronella candles, however, clip-on devices work by creating a fog of mosquito-repelling chemicals around you. This means that they will only be effective for times when you鈥檙e sitting still.
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Things That Don鈥檛 Work
While components of citronella oils may be effective repellants, citrosa houseplants are . Nor are the sonic mosquito repelling products that claim to play sound at frequencies that will drive mosquitos away. I鈥檒l let the authors of sum up the evidence for these products: 鈥淲e are not aware of any scientific study showing that mosquitoes can be repelled by sound waves and therefore we consider these devices as the modern equivalent of snake oil鈥�.
While synthetic mosquito lures that attract the bugs just as well, if not better, than humans , in practice mosquitos continue to be to humans even when these devices are used. Thus, their use is not by the Canadian Government. Likewise, handheld or mounted certainly exist and can be quite satisfying to use for revenge on the bugs that stole your blood, relying on them for protection is not .
You may have heard that eating bananas can make mosquitos more or less attracted to you. The claims of banana鈥檚 repelling power stem from their 听content, but tested the effects of vitamin B consumption on mosquito attraction and found absolutely no effects. In terms of bananas attracting power, those claims come from octenol content, a chemical that does indeed attract mosquitos. But, octenol isn鈥檛 unique to bananas, it鈥檚 found in many foods, and no studies have been done that prove consuming bananas does make you a bug-target, so keep on munching.
A subtler mistake you may make when selecting your mosquito repellant is to use a product that combines sunscreen and bug spray. While certainly convenient, the problem lies in sunscreen鈥檚 need to be reapplied much more frequently than mosquito-repellants. If both products are needed for an outing, it鈥檚 that you wait 20 minutes between applying sunblock and repellant.
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Basically, to avoid being a mosquito-target you should stay as scent-free as possible, wear light clothes, avoid bogs and use an effective repellent (such as those containing DEET or icaridin). Or, you could always stay inside- I hear its quite nice this time of year.
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