Blood type, metabolism, exercise, shirt color and even
drinking beer can make individuals especially delicious to mosquitoes.
You come in from a summer hike covered with itchy red
mosquito bites, only to have your friends innocently proclaim that they don’t
have any. Or you wake up from a night of camping to find your ankles and wrists
aflame with bites, while your tentmates are unscathed.
You’re not alone. An estimated 20 percent of people, it turns out, are
especially delicious for mosquitoes, and get bit more often on a consistent
basis. And while scientists don’t yet have a cure for the ailment, other than
preventing bites with insect repellent (which, we’ve recently discovered, some mosquitoes can become immune to over time), they
do have a number of ideas regarding why some of us are more prone to bites than
others. Here are some of the factors that could play a role:
Blood Type
Not surprisingly—since, after all, mosquitoes bite us to
harvest proteins from our blood—research shows that they find certain blood
types more appetizing than others. One study found that in a controlled setting,
mosquitoes landed on people with Type O blood nearly twice as often as those
with Type A. People with Type B blood fell somewhere in the middle of this
itchy spectrum. Additionally, based on other genes, about 85 percent of people
secrete a chemical signal through their skin that indicates which blood type
they have, while 15 percent do not, and mosquitoes are also more attracted to
secretors than nonsecretors regardless of which type they are.
Carbon Dioxide
One of the key ways mosquitoes locate their targets is by
smelling the carbon dioxide emitted in their breath—they use an organ called a maxillary
palp to do this, and can detect carbon dioxide from as far as 164 feet
away. As a result, people who simply exhale more of the gas over
time—generally, larger people—have been shown to attract more mosquitoes than
others. This is one of the reasons why children get bit less often than adults,
on the whole.
Exercise and Metabolism
In addition to carbon dioxide, mosquitoes find victims at
closer range by smelling the lactic acid, uric acid, ammonia and other
substances expelled via their sweat, and are also attracted to people with
higher body temperatures. Because strenuous exercise increases the buildup of
lactic acid and heat in your body, it likely makes you stand out to the
insects. Meanwhile, genetic factors influence the amount of uric acid and other
substances naturally emitted by each person, making some people
more easily found by mosquitos than others.
Skin Bacteria
Other research has suggested that the particular types and
volume of bacteria that naturally live on human skin affect our attractiveness
to mosquitoes. In a 2011 study, scientists found that having large amounts of
a few types of bacteria made skin more appealing to mosquitoes. Surprisingly,
though, having lots of bacteria but spread among a greater diversity of
different species of bacteria seemed to make skin less attractive. This also
might be why mosquitoes are especially prone to biting our ankles and feet—they
naturally have more robust bacteria colonies.
Beer
Just a single 12-ounce bottle of beer can make you more
attractive to the insects, one study found. But even though researchers had suspected
this was because drinking increases the amount of ethanol excreted in sweat, or
because it increases body temperature, neither of these factors were found to
correlate with mosquito landings, making their affinity for drinkers something
of a mystery.
Pregnancy
In several different studies, pregnant women have been found to attract
roughly twice as many mosquito bites as others, likely a result of the fact the
unfortunate confluence of two factors: They exhale about
21 percent more carbon dioxide and are on average about 1.26
degrees Fahrenheit warmer than others.
Clothing Color
This one might seem absurd, but mosquitoes use vision (along
with scent) to locate humans, so wearing colors that stand out (black, dark
blue or red) may make you easier to find, at least according to James Day, a
medical entomologist at the University of Florida, in commentary he gave to NBC.
Genetics
As a whole, underlying genetic factors are estimated to account for 85 percent of the variability
between people in their attractiveness to mosquitoes—regardless of whether it’s
expressed through blood type, metabolism, or other factors. Unfortunately, we
don’t (yet) have a way of modifying these genes, but…
Natural Repellants
Some researchers have started looking at the reasons why a
minority of people seem to rarely attract mosquitoes in the hopes of creating
the next generation of insect repellants. Using chromatography to
isolate the particular chemicals these people emit, scientists at the UK’s Rothamsted
Research lab have found that these natural repellers tend to excrete a handful of substances that
mosquitoes don’t seem to find appealing. Eventually, incorporating these
molecules into advanced bug spray could make it possible for even a Type O, exercising,
pregnant woman in a black shirt to ward off mosquitoes for good.
This Article was Written by Joseph Stromberg. He is a science reporter for Vox.com. He was
previously a digital reporter for Smithsonian.
Credts : smithsonianmag.com
