This episode of SciShow is supported by Brilliant. You can learn more at Brilliant.org/scishow [ ♪INTRO ] Ah, summer. Time to head outside for a hike, or a trip
to the lake, or maybe host a barbecue. But, no matter where you go, you’ll probably
get some unwanted attention from a certain flying blood-sucker. That’s right. It’s summer. It’s mosquito season, in the northern hemisphere
anyways . And every year it seems like there’s that
one person who gets the lion’s share of the bites. And that person is always me. And always on my right leg for some reason. We’re not going to get into the leg specificity
today, but there are some theories about why some people are mosquito magnets, a few of
them actually have some scientific backing. And, spoiler alert, it isn’t one single
trait, because mosquitoes don’t use one single cue to find their meals. So, here are five things that might be making
you a mosquito magnet — and what, if anything, you can do to lessen your appeal. Now, you’ve probably heard that mosquitoes
find their human targets by our exhaled breaths — and that’s true, but there’s even
more to it than that. What they’re attracted to isn’t that lingering
tuna sandwich you ate earlier but rather the carbon dioxide you breathe out, that’s part
of your normal metabolism. Scientists think that there are two ways CO2
increases your odds of getting bit. One, it ‘activates’ the mosquito — meaning
it triggers them to fly, and to fly more quickly. And two, it’s an attractant. Scientists think they use it to it orient
themselves to the source of the gas with the help of air currents — though they only
seem to do this when it’s released in bursts. Carbon dioxide is such a big part of how mosquitoes
find their targets that they have three types of smell-sensing cells in their mouth parts
that can detect it. They’re called Gr1, Gr2 and Gr3. In a 2014 study published in the journal Cell,
scientists showed just how important these cells are by creating genetically modified
Aedes aegypti mosquitoes whose Gr3 sensory cells didn’t work. Those modified mosquitoes no longer got all
excited when CO2 was puffed into the air. And, they were about 15% worse than their
unmodified relatives at hunting out a person in a large, enclosed area. But what’s even more interesting was that
the mosquitoes lacking their Gr3 cells were also no longer attracted to other cues that
help them find hosts. That suggested that carbon dioxide might actually
have a third role as a gatekeeper of sorts for other attractants. And that makes sense, because it’s a pretty
good indicator of animal life. So, if you don’t want to get bit, you could
just stop breathing all the time. Easy peasy. Except...the mosquitoes lacking the Gr3 sensor
could still find a target at close range. And that suggests CO2 draws the insects in
from a distance — while something else helps them zero in when they get close to their
target. And obviously, I was joking about the whole
not breathing, but while you can never emit zero carbon dioxide, things that make you
breathe more or more deeply could increase your attractiveness to mosquitoes, things
like, for example pregnancy. Because of course you need to attract more
mosquitoes on top of everything else you’re dealing with when there’s a fetus growing
inside you. And this also applies to exercise, which causes
you to breathe out more CO2. So you might come home with a few more bites
after a run than if you just went for a walk. Speaking of running, that nice glistening
sweat you produce when exercising can also draw mosquitoes in. Although moisture is an attractant for them,
what they’re mostly sensing is how you smell. Many of the chemicals in your sweat are considered
volatile compounds, meaning they can easily turn into a vapor. This includes things like lactic acid, amines,
sulfides, and carboxylic acids. And most of these are formed by the communities
of bacteria that live on your skin. So part of the mosquito magnet equation has
to do with these bacterial communities. People who have more skin-dwelling bacteria
have been shown to be more attractive to African malaria mosquitoes, for example. And one of those sweat compounds in particular
— lactic acid — might play a bigger role in mosquito attraction than the others. In a 2001 study in the journal Chemical Senses,
researchers took sweat samples from 4 volunteers and ranked them from most loved by mosquitoes
to least loved. The popular people were always popular: mosquitoes
consistently buzzed to their samples, even though they were collected on 28 different
days over the course of a year. And that seemed to be because of lactic acid
— the most attractive sweat had between three and five times more of it than the least
attractive. To test this idea, the researchers added lactic
acid to samples that weren’t that attractive, and low and behold, the mosquitoes suddenly
thought those sweats are great. More than 3 times as many mosquitoes chose
an altered sweat sample over their previous favorite. And that might have something to do with a
special lactic acid sensor in a mosquito’s antenna called Ionotropic Receptor 8a, or
just Ir8a for short. When scientists genetically engineered mosquitoes
to have a messed up Ir8a receptor, most didn’t fly towards samples of sweat containing lactic
acid in a wind tunnel or towards sweaty human subjects. And while there’s some evidence that exercise
raises lactic acid levels in a person’s sweat, in the end, it really comes down to
how smelly you are — and that comes down to a complex mix of your genetics, microbiome,
and hygiene behaviors. Mosquito bites aren’t just annoying. Every bite has the potential to pass along
mosquito-carried infections too — nasty stuff like encephalitis, West Nile virus,
yellow fever, and, of course, malaria. But what’s even more disturbing is that
these pathogens seem to change something about people to make them more attractive to the
mosquitoes that spread them around. For example, a 2005 study in PloS ONE found
that more mosquitoes were attracted to kids carrying the transmittable stage of malaria
than to kids who had been naturally infected with a non-infective stage or those who weren’t
infected at all. These differences disappeared when they treated
all the kids with an antimalarial, so the children’s individual mosquito attractiveness
wasn’t at play. Although pretty scary, this finding isn’t
that surprising. There are lots of examples in the animal world
of parasites manipulating their host to help them spread. The big question is what the pathogen is changing
to make the person it’s infecting more attractive. Scientists think it ultimately comes down
to odor, and a 2014 study using mice backed up that hypothesis. Researchers collected odor samples from both
infected and non-infected mice over the course of a malaria infection. During the later stages of infection, when
the parasite is transmittable, the mice produced more smelly chemicals than in the early, non-transmittable
stages — and were more attractive to the mosquitoes. And when researchers created different mixes
of those chemicals and applied them to healthy mice, those mice also became mosquito magnets. The scientists were eventually able to figure
out which chemicals were drawing the mosquitoes in — 3-methyl butanoic acid, 2-methyl butanoic
acid, hexanoic acid, and tridecane, in case you were wondering. But, of course, this was in mice. So all the usual caveats about animal research
apply. Still, it shows there are infection-related
changes that lure mosquitoes in. And that means studies involving humans might
be able to figure out exactly how these infections make us more prone to bites. Most of the things that make you a mosquito
magnet aren’t all that easy to change. But one thing is: your clothes. A bunch of studies dating all the way back
to the 1900s have shown that mosquitoes love to land on dark colored surfaces — everything
from painted barn roofs to boxes and, of course, clothing. One of the earliest studies from 1947 had
a guy stand in a mosquito infested room wearing either a black, white, green, red, yellow,
blue or tan shirt, while the researcher counted how many mosquitoes landed on him. Black, blue and red were the most attractive
to mosquitoes — they didn’t care as much for yellow or white. A later study from the early 1980s using differently-colored
funnel traps found the same thing. It also found that how much light reflected
off the cloth determined how attractive the traps were — basically, mosquitoes like
things that aren’t super reflective. Also, the mosquitoes seemed to like shorter
wavelengths of light, in the 400 to 600 nanometer range — basically, violet to orange colors
— while anything with a wavelength over 600 nanometers was pretty much a no go. So, you could opt for a light colored outfit
or anything reflective — maybe it’s time to just bust out that sequined dress that
turns you into a living disco ball. For clarity, scientists haven’t explicitly
tested whether sequins or shimmery fabrics keep them at bay, but there’s every reason
to think they should. And it’s thought that visual cues like color
help mosquitoes spot a target from a greater distance, particularly during the day. One of the myths going around is that dark
fabrics absorb more heat and so it’s the temperature, not the color itself, that they
love. But a 2019 study found mosquitoes go for dark
objects regardless of how warm they were. That study needs to still be vetted by the
scientific community but if it holds up, it might help scientists figure out how much
of a role these different cues play. Another reason black is so popular is probably
fairly simple: dark-colored objects generally stand out more against their background — to
a mosquito, anyway. So, if shimmer isn’t your thing, you could
go the other way and wear something that will help you blend in with your surroundings — maybe
go cammo! I’ve got some bad news for those summer barbecues: turns out that if you’re drinking
booze, you’re probably making yourself more of a mosquito target. This idea has been around for a long time,
but it wasn’t really tested in a controlled manner until the early 2000’s. A 2002 study, published by the American Mosquito
Control Association, found that more mosquitoes landed on subjects after drinking a glass
of beer than before. The people were drinking beers, not the mosquitos But, the researchers couldn’t pinpoint why. Their first thought was changes to skin temperature,
since mosquitoes sense and are attracted to heat. Or, that the animals literally like the smell
of alcohol. The trouble is, they didn’t find any links
between how many mosquitoes landed on the people and how warm they were or how much
ethanol they had in their sweat. A study in 2010 backed up the beer-increases-attractiveness
finding. And again temperature didn’t seem to be
a mediating factor — in fact, on average, people were colder after drinking. That led the researchers back to this idea
of smell. But it wasn’t the smell of ethanol itself,
they argued. Rather, they suggested that as alcohol metabolizes,
it increases other chemicals in a person’s breath or sweat that make them a tastier-smelling
target. Though it’s not clear what these other chemicals
are. They also hypothesized that mosquitoes could
have evolved to seek out these particular aromas because they indicate lower physical
defenses — basically, booze makes you less coordinated, so you are bad at slapping the
mosquito. That sounds pretty logical, but a different
study found no link between how defensive a person is — that is, how much they tried
to swat away a mosquito — and how many times it tried to land on them. Which isn’t conclusive evidence against
the idea, but it certainly doesn’t support it. Another potential explanation is that a boozed-up
bloodstream makes for a more nutritious meal somehow, so mosquitoes have evolved a way
to detect that — though, no study to date has tested this directly. Whatever the reason, it might be wise to skip
the brewskis if you’re hanging around outdoors. Or, at least, cover up if you insist on a
beer while barbecuing. Just head to toe, wear one of those beekeeper
outfits. In the end, you cannot completely take yourself
off a mosquito’s radar — without bug repellent, anyway. But you can make yourself a little less tempting
— like, by wearing the right clothes, or being the Designated Driver. And there’s something else you might be
able to do to lessen your chance of getting bit: offer the mosquitoes around you a different
snack. Research published in 2019 in PLoS Biology
found that feeding tiger mosquitoes sugar lessened their attraction to people. See, the whole reason female mosquitoes bite
is that a blood meal gives them the extra protein and nutrients they need to develop
their eggs. And in this case the sugar seemed to be meeting
that nutritional need, though it’s not a 100% clear whether the sugar helped the female’s
eggs develop or not. Most intriguingly: sugar triggered a response
in the mosquitoes’ genes that’s similar to what happens after they feast on blood. So maybe putting out some hummingbird feeders
or dishes of cotton balls soaked with sugar-water will make the mosquitoes near you less interested
in your blood. Though, yes, it might be attracting mosquitos
around you and also you’d be fueling those mosquito baby-mommys. So I guess it’s not a perfect solution. Still, scientists are excited by this research
because it means they might be able to identify new genes involved in the mosquitoes’ human-seeking
behavior, which could reveal new ways to control their biting. Because, in the end, while no one likes being
bitten by mosquitoes, some itchy bumps are the least of our worries. Those mosquito-carried diseases kill around
a million people every year. So finding new and better ways to prevent
mosquito bites — especially for those who are magnets — could save millions of people. Making those summer outdoor activities all
that more enjoyable is just a bonus. Speaking of fun summer activities, if you
need something to do on your next road trip, you could try and stump your car with one
of Brilliant’s Daily Challenges. It will probably kill way more time than a
game of I Spy, and you’ll get to learn something about science, engineering, or math. One of the latest challenges, for example,
was about what kind of tire tracks different unicycles leave. It was a tough one! Brilliant puts out new Challenges every day,
and you can get the latest ones for free. If you sign up for a Premium membership, you’ll
also get access to the entire archive — which should be more than enough to get you to your
destination. If you’re one of the first 200 people to
sign up at Brilliant.org/SciShow, you’ll get 20% off that annual Premium subscription,
and you’ll be supporting SciShow along the way. So, thank you! [ ♪OUTRO ]
People always say, oh there’s so many things you can learn by watching YouTube videos. Yes, but I rage quit after 2 minutes because the host likes to hear the sound of their own voice. Give me a quick intro, then give me the juice.
Breathing
Sweat
Mosquito-Borne Disease
Dark Colored Clothes
Drinking Alcohol
I made it about a minute in. How'd i do?
Can we make tl;dw a thing?
Someone is shadow banned here
All these people talking about how long the vid is but scishow is known for very long and thorough explanations. It's not the most accessible but still very interesting if you care about the research behind it.
Mosquitoes love two things more than anything else!
Carbon dioxide, which we not only breathe out, but is also released through our skin!
Heat, which we are constantly giving off.
If you want to avoid mosquitoes, wear bug spray with DEET or that contains lemon eucalyptus oil.
looks like i'm gonna have to give up wearing dark clothes while i day drink at the park. shit.
The length of this video angers me. That is all.