Repellents are still the best defense -
Repellents containing the chemicals DEET
or picaridin are still the best defense
against mosquitoes, ticks and biting flies and the
diseases they can spread. Repellents can also be
combined with an insecticide applied to clothing and
gear for maximum protection.
are still your best defense against biting pests
like mosquitoes, black flies, biting midges,
chiggers, ticks and the diseases they may carry.
However, there is a lot of confusion about which
repellents are most effective, safest and the best
way to use them.
There are now two different synthetic
chemical ingredients used in formulating insect
repellents that are roughly equivalent in
effectiveness, namely DEET and picaridin.
There are also a number of natural products that
claim repellency but are generally less effective.
Insect repellents are compared on the basis of how
long they remain effective after application and how
much they reduce the frequency of bites. There's
generally a direct relationship between the
concentration of active ingredient and how long the
repellent remains effective.
common misspelling: mosquito repelant;
Yellow fever mosquito
Line drawing of adult mosquitoes.
Since the 1950's most insect
repellents were made from the chemical DEET
(N,N'-diethyl-3-methylbenzamide) which had been
developed by the military. Maximum strength
repellents contain 100% DEET but some use
concentrations as low as 5%. DEET is an oily liquid
that can be applied to skin or clothing but it
dissolves certain plastics and synthetic fabrics
such as eyeglass frames and tent fabrics.
After 50+ years of DEET being the only
really effective insect repellent a new contender has
entered the arena. Picaridin, also called
icaridin, is a colorless and odorless liquid that
equals the effectiveness of DEET but is less
irritating and does not dissolve plastics
or damage synthetic fabrics.
What repellent should you use, and
Gardeners: should use a
DEET-based or picaridin-based repellent when working
in areas where chiggers or mosquitoes
may be a problem. A low concentration (less than 10%)
product will provide several hours of protection.
Hikers, hunters and campers:
should take special precautions against ticks
since they are more likely to pass through tick
habitat. Treat clothing and camping gear with permethrin
and exposed skin with a DEET or
picaridin-based repellent. These combination
treatments will protect against mosquitoes,
black flies, biting midges and ticks.
Horse owners: (yes, horses need a
biting fly repellent too!) treat horses with fly
repellents whenever mosquito or biting fly pressure is
high. Even if horses have been vaccinated against West
Nile virus these repellents will reduce annoyance from
mosquito bites and protect against biting flies that
cause sweet itch. See What
is Sweet Itch in Horses?
Using repellents safely
Like any insecticide or medication you
should use the least amount and lowest concentration
of insect repellent that is still effective in order
to avoid potential side effects. Products are
available from 5% - 100% active ingredient. For most
insect repellents exceeding concentrations of 50%
offers very little added benefit and may increase
health risks especially for prolonged use. Products
used on children should generally not exceed 10-20%.
I prefer products in non-aerosol sprays
or lotions and in concentrations less than 50%.
Non-aerosol spray pumps allow for more careful,
targeted application and produce a larger droplet size
that is less likely to be inhaled. See this Centers
for Disease Control Factsheet About Mosquito Repellents
for additional suggestions and precautions regarding
the use of insect repellents.
Treat clothing and camping gear with
Permethrin is an insecticide
that can be safely applied to clothing and gear, but
not skin, to protect against mosquitoes,
black flies, chiggers, ticks, and other biting
pests. Permethrin has been used by the military for
many years to treat fabrics and is now available to
the general public. It can be used by hunters,
hikers, campers and others that venture into areas
where mosquitoes or black flies are a problem. The
combination of permethrin-treated clothing and a
DEET or picaridin-based repellent applied to skin is
highly effective. Treated cloth remains effective
for several weeks even when washed.
markets a permethrin spray that can be
applied to clothing, tents, backpacks and so forth.
What about citronella oil and oil of
Citronella is a plant oil and natural
insecticide. It is widely used in "non-DEET" based
repellents and in mosquito repellent candles.
Citronella oil has not been tested as extensively as
DEET or the new picaridin-based repellents. However,
in tests that have been done citronella oil only
provided protection when applied to the skin and the
protection was short term compared to DEET and
picaridin. Oil of lemon eucalyptus is another natural
plant oil that is about as effective as low
concentration DEET according to the Centers for
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