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Are You a Mosquito Magnet?
Experts try to crack the code behind why mosquitoes
like some humans more than others.
By Elizabeth Heubeck
WebMD Feature
You're flipping burgers for the neighborhood
barbecue, and the mosquitoes have already begun
their feast -- on you. As you swat madly at the
pests, you notice other folks seem completely
unfazed. Could it be that mosquitoes prefer dining
on some humans over others? This may clear up the
mystery.
It's
true. Mosquitoes do exhibit blood-sucking
preferences, say the experts. "One in 10 people are
highly attractive to mosquitoes," reports Jerry
Butler, PhD, professor emeritus at the University of
Florida. Incidentally, it's not dinner they're
sucking out of you. Female mosquitoes -- males do
not bite people -- need human blood to develop
fertile eggs. And apparently, not just anyone's.
Who Mosquitoes Like Best
While researchers have yet to pinpoint what
mosquitoes consider an ideal hunk of human flesh,
the hunt is on.
"There's a tremendous amount of research being
conducted on what compounds and odors people exude
that might be attractive to mosquitoes," says Joe
Conlon, PhD, technical advisor to the American
Mosquito Control Association. With 400 different
compounds to examine, it's an extremely laborious
process.
"Researchers are just beginning to scratch the
surface," he says.
Scientists do know that genetics account for a
whopping 85% of our susceptibility to mosquito
bites. They've also identified certain elements of
our body chemistry that, when found in excess on the
skin's surface, make mosquitoes swarm closer.
"People with high concentrations of steroids or
cholesterol on their skin surface attract
mosquitoes," Butler tells WebMD. That doesn't
necessarily mean that mosquitoes prey on people with
higher overall levels of cholesterol, Butler
explains. These people simply may be more efficient
at processing cholesterol, the byproducts of which
remain on the skin's surface.
Mosquitoes also target people who produce excess
amounts of certain acids, such as uric acid,
explains entomologist John Edman, PhD, spokesman for
the Entomological Society of America. These
substances can trigger mosquitoes' sense of smell,
luring them to land on unsuspecting victims.
But
the process of attraction begins long before the
landing. Mosquitoes can smell their dinner from an
impressive distance of up to 50 meters, explains
Edman. This doesn't bode well for people who emit
large quantities of carbon dioxide.
"Any
type of carbon dioxide is attractive, even over a
long distance," Conlon says. Larger people tend to
give off more carbon dioxide, which is why
mosquitoes typically prefer munching on adults to
small children. Pregnant women are also at increased
risk, as they produce a greater-than-normal amount
of exhaled carbon dioxide.
Movement and heat also attract mosquitoes.
So
if you want to avoid an onslaught of mosquito bites
at your next outdoor gathering, stake out a chaise
lounge rather than a spot on the volleyball team.
Here's why. As you run around the volleyball court,
the mosquitoes sense your movement and head toward
you. When you pant from exertion, the smell of
carbon dioxide from your heavy breathing draws them
closer. So does the lactic acid pouring from your
sweat glands. And then -- gotcha.
Where Mosquitoes Lurk
Even
if your body chemistry doesn't attract mosquitoes,
where you're located might.
Some
of the worst mosquito populations exist along
coastal areas, Conlon tells WebMD. And being several
miles inland does not guarantee your safety from the
pests. "They'll fly 40 miles for a meal," Conlon
says.
While any water source is potential breeding grounds
for mosquitoes, they much prefer stagnant water. So
if you crave a mosquito-free water oasis on your
property, forgo the backyard pond and seek out a
babbling brook instead.
"Even in a desert area, mosquito biting tends to be
intense around a water source," Conlon says.
Can
you find respite high in the mountains? Don't count
on it. Although they're generally not active below
55 degrees Fahrenheit, mosquitoes have been sighted
in the Himalayan Mountains, Conlon tells WebMD.
How
about cold climates in places such as Alaska? You're
safe for most of the year. But, says Conlon,
mosquitoes flock there for a brief, three-week
period between July and August.
"The
Arctic National Refuge is one big bog," Conlon
explains, making the mosquito population there
second only to that in the Florida Everglades.
With
a long track record -- mosquitoes have been around
for 170 million years -- and more than 175 known
species in the U.S., these shrewd summertime pests
clearly aren't going to disappear any time soon. But
you can minimize their impact.
Keeping the Bite at Bay:
Chemical-Based Repellents
Plenty of mosquito repellents line the shelves of
drugstores and supermarkets each summer, but they're
not all created equally.
The
majority of available mosquito repellents derive
their effectiveness from chemicals. Protecting the
public from mosquitoes since 1957, DEET continues to
be the chemical of choice used in repellents. In
repeated studies, it's been proven the most
effective chemical repellent on the market.
Repellents with 23.8% DEET (most formulas contain
between 10% and 30%) protect wearers for about five
hours, according to a recent study led by Mark
Fradin, PhD, a researcher with Chapel Hill
Dermatology. The American Academy of Pediatrics and
other experts suggest that it is safe to apply
repellent with low concentrations of DEET (10% or
less) to infants over 2 months old.
In
2005, the CDC began recommending alternatives to
DEET for repelling mosquitoes. Picaridin, which is
new to the U.S., has been used worldwide since 1998.
It has proven to be as effective as DEET but is more
pleasant to use because it has a light, clean feel
and is virtually odorless. Picaridin is safe for
children older than 2 months. This substance is
marketed as Cutter Advanced.
The
other new CDC recommendation is oil of lemon
eucalyptus, which is available under the Repel brand
name. This product offers protection similar to low
concentrations of DEET. Lemon eucalyptus is safe for
children older than 3 years.
The
chemical IR3535, better known as Avon's
Skin-So-Soft, has also been marketed as a repellent
in recent years. To date, research shows it's much
less effective than DEET.
Safety of DEET Repellents
Just
how safe is it to coat yourself in a chemical-based
product like DEET just to keep from getting bitten
by mosquitoes?
"DEET
has been in use for over 40 years and has a
remarkable safety record. Only few hospitalizations
have been reported, mainly due to gross overuse,"
Conlon tells WebMD.
The
Environmental Protection Agency (EPA), after
extensively assessing the safety of DEET, concluded
that "as long as consumers follow label directions
and take proper precautions, insect repellents
containing DEET do not present a health concern."
The agency does, however, offer the following safety
strategies for DEET use:
-
Follow label directions and precautions.
-
Use sparingly.
-
Avoid spraying on or near open skin, eyes,
mouth, and nose, under clothing, or near food.
-
Wash treated skin with soap and water.
The
American Academy of Pediatrics (AAP) provides these
additional recommendations for DEET use on children:
-
Select the lowest concentration effective for
the amount of time spent outdoors.
-
Avoid use on infants under 2 months of age.
-
Avoid repeated applications, which may increase
the potential toxic effects of DEET.
Alternative Repellents
Want
to avoid chemical-based repellents altogether?
Alternatives do exist, with one or two showing
promise.
"Of
the products we tested, the soybean oil-based
repellent was able to protect from mosquito bites
for about 1.5 hours," Fradin reports. He and fellow
researchers found other oils -- citronella, cedar,
peppermint, lemongrass, and geranium -- provide
short-lived protection at best. Oil of eucalyptus
products, however, may offer longer-lasting
protection, preliminary studies show.
Hate
to spray or slather yourself with any product,
either chemical- or plant-based? Mosquito traps, a
relatively new product, may be the answer. They work
by emitting substances that biting mosquitoes find
attractive -- such as carbon dioxide, heat,
moisture, and other mosquito-friendly byproducts.
They attract, then trap or kill female mosquitoes.
When placed strategically near breeding spots, "they
have knocked (mosquito) populations down," Conlon
tells WebMD.
So
is it worth the effort it takes to prevent
mosquitoes from nipping at your ankles? Yes, if you
don't want to be bothered by bouts of
mosquito-induced itching all summer long.
Certainly, if you are one of the few unfortunate
souls in whom mosquito bites result in severe
allergic reactions. And most definitely if you
believe you're likely to be exposed to potentially
fatal mosquito-borne diseases, some of which are
becoming increasingly common.
Take
the mosquito-transmitted West Nile virus, which
Conlon says "is probably here to stay." And with it,
the age-old, ever-adaptable mosquito.
©
WebMD. All rights reserved.
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"People with high concentrations of steroids or
cholesterol on their skin surface attract
mosquitoes" |
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