“Finding what attracts mosquitoes will ultimately help us find ways to control them.” -Ulrich R. Bernier World travel and mosquitoes go together, and devising ways to limit the frequency of being bitten by them is part of the standard operating procedure of any traveler. Knowing what attracts mosquitoes to your flesh is the first step to figuring [...]
“Finding what attracts mosquitoes will ultimately help us find ways to control them.” -Ulrich R. Bernier
World travel and mosquitoes go together, and devising ways to limit the frequency of being bitten by them is part of the standard operating procedure of any traveler. Knowing what attracts mosquitoes to your flesh is the first step to figuring out methods to keep them away — which is clutch in this perpetual battle of travel. To arm ourselves with more ammunition in this fight, Vagabondjourney.com turns to recent scientific findings which are beginning to put together a picture of how mosquitoes find their prey as well as what, in particular, attracts them to humans. I also asked professor Niels Verhulst, from Wageningen University’s Laboratory of Entomology, practical questions about his recent study which shows how natural human scents attract mosquitoes and what people can do to decrease their attractiveness to this rather annoying and potentially deadly insect.
What attracts mosquitoes to humans
When with a group of people in a mosquito infested area it is clear that they tend to me drawn towards some individuals more than others. I’ve heard all sorts of projected explanations — It’s because you’re wearing deodorant, it’s because they like the soap you use, it’s because of your blood type, it’s your perfume, it’s because you don’t shower, it’s because you did shower, it’s because you’re a woman etc . . . — but now I’m looking at the science behind this phenomenon in order to come up with a strategy to become less attractive to mosquitoes and, hopefully, to be bitten with less frequency.
There are five main elements that attract mosquitoes to their human prey:
- Exhaled carbon dioxide/ octenol
- Bacteria/ body odor
- Secretor status/ blood type
- Lactic Acid
- Body heat
Scent is a prime mosquito attraction
One of the prime ways that mosquitoes are attracted to humans is through their scent. There are various smells emitted from the body, but the main ones that mosquitoes apparently hone in on are exhaled carbon dioxide and octenol, bacteria on the skin, a person’s secretor status, blood type, and lactic acid secretions. Mosquitoes have several proteins in their antennae and heads that catch some of the odorants and gasses that humans emit when we exhale and secrete from our skins. Like flashing lights in the dark, these scents stand as beacons for all mosquitoes in “smelling” range.
“So far, we have found more than 340 different chemical scents produced by human skin, and some of these attract mosquitoes,” says ARS chemist Ulrich R. Bernier.
One of the main functions of most mosquito repellents is to mask a person’s natural scents so as to make them less conspicuous. Below, we will investigate some of these scents and their causes in our attempt to devise methods to become less attractive to mosquitoes.
Exhaled carbon dioxide and octenol
It has been known for a long time that mosquitoes are attracted to carbon dioxide, which humans and other animals exhale. The more of this gas you exhale the more you stand to call in a crowd of mosquitoes. But carbon dioxide, in and of itself, is not enough to attract loads of mosquitoes, as there are many other events in nature that also produce this gas. Rather, it is the combination of sensing this this gas combined with another that humans exhale that brings in the mosquitoes in droves. This gas is called ocetnol, it is an alcohol described as “cow’s breath in a can,” and it can excite mosquitoes within a 100 foot range.
The amount of carbon dioxide and ocetnol that you exhale is determined by your biology, and there isn’t really too much you can do about it short of not breathing — which isn’t really a viable long term option to say the least.
While a human can’t do much about exhaling carbon dioxide and octenol, there are some strategies for limiting another scent that also serves to bring in mosquitoes: body odor. While your funk may cause people to avoid you, it is one of the elements that mosquitoes find most attractive in a human. Body odor is caused by bacterial colonies on the skin, and without bacteria our sweat would be scentless. Generally speaking, the stronger a human smells the more they stand to attract mosquitoes. As put by professor Verhulst: “The most important malaria mosquito Anopheles gambiae is very anthropophilic (prefers to bite humans). It therefore not only uses carbon dioxide like other mosquito species but also human specific odours, produced by bacteria.”
I asked professor Verhulst if bathing with anti-bacterial soap could be a method for making oneself less attractive to mosquitoes, and he replied that, “Incubated sweat is more attractive to mosquitoes than fresh sweat because of the bacteria in the sweat that produce these attractive compounds. Washing yourself regularly may help, but other precautions may work better like wearing protective clothing, using repellents, using bed nets etc. We are now developing attractive (bacterial) compounds that may be used in traps and repellents that may keep the mosquitoes away.”
Secretor status/ blood type
For the past couple of decades scientists have been finding links between blood type and a person’s attractiveness to mosquitoes. So the “they like the taste of my blood” position is actually backed up by scientific fact. A study that was published in Nature (Wood and Dore, 1972) demonstrated that mosquitoes are most drawn to people with type O blood while being less attracted to those with type A. This findings of this study were re-confirmed in 2004 by a Japanese investigation.
Though these discoveries were only this the start of this investigation, as it was found soon after that it is not just that mosquitoes desire certain blood types over others, but that they are hyper-drawn to people who are known as “secretors.” A secretor is a person who, simply put, secretes saccharides (sugar based chemicals) and antigens through their skin which can indicate their blood type. Around 80% of the US population have the secretor (Se) gene. First and foremost, mosquitoes are attracted to secretors, then, with everything else being equal, will prefer people with type O blood and show more avoidance towards those with type A. Therefore, a type A secretor will be more attractive to mosquitoes than a type O non-secretor, but a type O secretor emits a scent signal that is most prone to attract mosquitoes.
But this does not mean that people with type A blood have a special pass when dealing with mosquitoes, as this blood type has been shown to be more prone to contracting malaria. So while it is true that type A people are less attractive to mosquitoes than other blood types, the probability of them getting malaria from these bites is greater.
There is little that anybody can do about their blood type and whether or not they are secretors. The adage that mosquitoes love some people more than others is true, and there is often little that anyone can do about it.
Lactic acid is naturally emitted through the skin of humans when active or eating certain foods. Mosquitoes have also cued in on the smell of this chemical as a sign of fresh meat, so to speak, and they will be more attracted to a person who has more of a lactic acid build up on their bodies than one who doesn’t. To lessen the amount of this chemical on your skin, be sure to wash with soap after exercising and dry off thoroughly.
Mosquitoes have highly developed thermosensors that can detect body heat, and the warmer your body is the more attracted mosquitoes are going to be to you. Drinking alcohol is a sure shot way to make yourself more desirable to mosquitoes, as this liquid quickly raises a person’s body temperature and makes them “flush” as they metabolize it.
The fact that mosquitoes can detect body heat is good to know when in tropical climates that are infested with mosquitoes. Practically speaking, washing regularly to cool off is a clutch move to lessen your attractiveness to mosquitoes — just be sure to dry off when done, as mosquitoes love moisture.
It is no secret that mosquitoes are attracted to moist locations. They breed and lay eggs in shallow pools of water, and moisture on a person’s skin and the vapor in their breath is a prime invitation for mosquitoes to stop by for a meal. Even relatively small amounts of water will attract mosquitoes, as it could mean a blood source or possible breading area. To prevent against this, make sure your skin is as dry as possible, wipe away sweat, towel off after bathing and swimming, and keep in mind that you will exhale more water vapor as you engage in strenuous activity.
It has been shown that mosquitoes can see their prey from 30 feet away judging by the fluctuations of light waves in their proximity. Not moving when and where mosquitoes abound is often not really an option, but limiting unnecessary movement may help to make you less attractive to these blood suckers.
The mosquito is somewhat of a Gothic creature, preferring not only dark places but dark colors as well. Wearing clothing that is of darker shades will attract mosquitoes more than light colors.
Pregnancy seems to be a big winner for hungry mosquitoes. Expecting mothers exhale 21 percent more carbon dioxide and tend to be over a degree Fahrenheit warmer in the belly area than other people. So when pregnant, keep in mind that you are going to attract more mosquitoes.
Mosquito bite prevention tips
There is no absolute way to prevent every and all mosquitoes from biting you. Rather, mosquito bite prevention is an endeavor of trying to lessen the amount of bites than trying to eliminate the possibility all together. As professor Verhulst said above, a multi-faceted approach towards inhibiting mosquito bites is often the best strategy anyone can take. The methods outlined below should be used in tandem with each other, using as many concurrently as is applicable in a given circumstance.
Know the real risks of mosquito borne illness in the immediate regions you are traveling in
Know the risks for serious mosquito borne illnesses in the regions you’re traveling in. Just because a place has mosquitoes does not mean that they pose a serious health risk, and there are also many different types of dengue fever and malaria (go to Different Types of Malaria and Tips for Prevention). With both of these diseases, the seriousness varies depending on what type you get, so measuring this risk and its prevalence rate in your current location is key. Keep in mind that most travel clinics in the USA will just show you a map of the world that has these huge areas colored in and tell you that deadly malaria is epidemic there. The reality is far more specific than this: in some of these colored in regions malaria is rampant, in others it hardly even exists, while still in some other areas malaria exists but is not generally the life threatening variety.
Taking malaria meds and using DEET carry certain health risks in and of themselves, so measure these against that of getting a serious mosquito borne illness. For the vacationer going into the tropics for a week or two, covering up with DEET and taking anti-malaria meds may be the best option, but for a long term traveler who is living in malaria/ dengue regions for years on end, the side effects of extended use of prophylaxis and the continuous use of repellent may prove a greater health risk than the diseases they prevent against. If you’re going to be in the tropics long term, find out the risks of mosquito borne illnesses with each locale you travel to and adjust your prevention methods accordingly. To find out the risk for these diseases walk in to a local medical clinic and ask the doctors and nurses how often they see cases of malaria etc . . .
Always travel with and use a mosquito net
When in areas where mosquitoes are rampant or where they could potentially carry disease, always be sure to use a mosquito net. Being under a mosquito net when sleeping or otherwise idle is probably the single best way to prevent being bitten by mosquitoes outside of bathing yourself in high percentage DEET. If mosquitoes can’t land on your body they can’t bite you, and a properly set up mosquito net can keep a healthy distance between you and the bloodsuckers. For added effect, treat your mosquito net with permethrin or another spray designed to deter mosquitoes. If you want to sit or sleep outside, make a mosquito net for a hammock.
Mosquito net videos
Wear protective clothing
Wearing light colored long sleeve shirts, long pants, and a hat is another way to inhibit mosquitoes from biting. The effect that this will have depends on the type of mosquito you’re dealing with, as some can bite through clothing while others cannot, but whatever is the case, clothing at least makes it more difficult for the little buggers to get you. When in tropical areas with a high mosquito prevalence I usually wear a cotton t-shirt with a long sleeve light weight cotton shirt over top of it and khaki pants. It also helps to treat your clothes with permethrin or another anti-mosquito spray that is designed for clothing. Though I know that simply wearing protective clothing will not prevent mosquitoes from biting I also know that it will lessen the frequency that I will be bitten, and this is the main intent.
The catch-22 of covering up in clothing is that mosquito infested areas also tend to have relatively hot temperatures, and, as the logic goes: the more clothing you wear in hot climates the hotter you will be, and mosquitoes are attracted to heat, sweat, and the stronger smells that emit from a sweating person. So a balance between covering up in clothing and becoming overheated should be found.
Use an electric fan
Locals in tropical regions around the world often swear by this method of keeping mosquitoes off of a person. I’ve tried this method on many occasions and found it to be useful: directing the output of an electric fan onto your body is a way to help keep mosquitoes at bay. This method not only makes it difficult for mosquitoes to fly through the artificially derived wind to get to you but it also may disperse your breath and scent as well, making it more difficult for them to hone in on you. It does not take a science lab to test this hypothesis, just flip a fan on and off as you lay in bed one night in the tropics and find out for yourself how much the fan method works.
I rarely use mosquito repellent, though I know that my position is atypical, and most travelers are not as adverse to these chemicals as I am. A 10% DEET is often recommended as being a balance between repelling mosquitoes and not being too poisonous, but in deep rainforest areas a stronger percentage is often needed to be effective. Seriously speaking, a strong DEET is probably the best preventative against mosquitoes that exists.
Carry a supply of prophylaxis and take or buy locally if you suspect malaria
I stand out on a limb when I recommend against taking malaria prophylaxis long term. Rather, I recommend selective use or keeping an emergency supply in case you suspect that you may have caught malaria (the cure is often the same medicine as the prophylaxis). Be aware of the true malaria prevalence rates in the regions that you are traveling in, and if you are going to be in an area of heightened risk short term (meaning a week or two) taking a prophylaxis may be a good idea — and this medicine can often be purchased locally for dirt cheap. The long term risks of taking malaria prophylaxis is still up for debate, but it is not my impression that taking potentially harsh medication regularly for months or years on end doesn’t presents some type of pernicious health impact. I have not taken a malaria prophylaxis since 2001, and I’ve spent many years in tropical climes since then. The choice though, as always, should be left up to the individual.
Mosquitoes are truly well rounded predators. They have evolved many mechanisms for finding and sucking blood from their prey and instinctively knowing the best ways to go about doing so. Mosquitoes seem to be attracted to just about any attribute that marks you as a live human: body order, scents derived from blood type, body heat, sweat, breath are all observable by skeeters looking for a meal.
While it is often not possible to get rid of many of the telltale signs of your species (their prey), there are things that you can do to cover them up. Washing the skin regularly can help to decrease bacteria derived scent, lactic acid, and sweat, which are all major attractions for mosquitoes. While keeping the skin dry, trying to keep cool, abstaining from alcohol, and covering the body with substances which mask its natural odors (such as garlic, DEET, and other insect repellents) are all ways to attempt to limit your attractiveness to mosquitoes. These methods combined with wearing protective clothing, placing a fan on you when idle, and using mosquito nets are all ways to lower the amount of times you’re bitten by mosquitoes and raise your chances of traveling safely in the tropics. Living with mosquitoes is a part of traveling in the forest regions of this planet, it’s a good thing that there are ways to prevent against being bitten.
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