|
Developed by the US Military and USDA after
researching thousands of compounds during the 1950s, billions of applications later DEET is still the most effective
insect repellent against mosquitoes and ticks.
|
How Deet Works
Insects such as mosquitoes are attracted to
their targets from a distance by carbon dioxide and lactic acid, which are given off by living things through breathing
and muscle activity. At close range, body heat and electrical stimuli help the insect home in on its subject, which
is why people are often bitten on the ankle, neck or other thin skin area of the body. Deet works by masking those
far off odors from living things, and then by confusing the insect at close range by interfering with its electrical
receptors. |
| Deet Repellents work through evaporation. This creates a vapor shield two to three inches above the area
of application. The presence of the repellent confuses insects so that they go away. Usually only a small amount
of repellent needs to be present on the skin to be effective. It is the delivery system or carrier material which
often determines how much repellent you must start with and whether or not re-application is required during your
exposure period. |
Deet Repellent Application
The EPA defines an application
of insect repellent as one gram of formula per 600 square centimeters (<94 square inches) of skin. If the formula used is 100% Deet then users would
be applying one gram of Deet. If the formula is a 20% Deet formula, there would be 0.2 grams of Deet and 0.8 grams
of carrier material. To achieve an application equivalent to 0.2 grams of Deet per 600 Cm2, the user could either
apply one gram of 20% formula or 2/10 gram of 100% Deet formula. |
How Much Deet Is Needed To Repel Insects?
Not much Deet needs to be present on the skin
at any one point in time to repel most insects. Research performed by the industry suggests between 0.005 and 0.01
grams of Deet per 94 square inches of skin is usually enough. Aggressive or swarming insects may require as much
as 0.015 grams. However, as Deet evaporates fairly quickly after application, much higher doses must be initially
applied to ensure that hours later enough Deet still remains on the skin to stay above that base repellency level. |
Deet Concentration and Repellency
Deet repellency rises sharply with concentration
up to around 30% Deet. Additional strengths up to 50% Deet gain nominal repellency, but over 50% Deet very little
additional effect is gained other than length of time. |
Other Ingredients In Deet Repellent
Most Deet formulas are mixed with alcohol
or water as their inactive ingredients. Aerosol formulas will contain propellant solvents. Some composite formulas
contain additional repellents and/or synergists as well as Deet, e.g. Broad Spectrum and Deet Plus which contain
R326 fly repellent and MGK264 synergist. Time-released Deet repellents contain polymers or proteins which break
down slowly in contact with skin. Composites can last longer than straight Deet formulas, and time-release formulas
such as Controlled Release will last much longer than comparable straight Deet formulations. |
Will Deet Damage My Clothes?
Deet is safe for skin and natural fiber clothing
such as cotton. Most man-made fibers (except nylon) may be damaged or stained by Deet. Deet will also stain, soften
or damage plastics, paints, varnishes and lacquers. Permethrin will not hurt any fabric and is the repellent of
choice for most clothing applications. |
Does Deet Irritate The Skin?
Deet is a skin irritant but
does not create a skin sensitivity. After a period of frequent use your skin may become
red, even sore to the touch, irritated by the presence of Deet. You do not however develop an allergic resistance
to Deet. If allowed time to recover, your skin will accept the presence of Deet again without rapidly developing
a rash. Continued use could again develop irritation. Deet has been well studied and people do not develop allergic
reaction or skin sensitivity to Deet. The amount of Deet which can be used prior to developing
skin irritation varies from person to person. |
Deet And Skin Absorption
To date absorption studies indicate
that the body releases all Deet which it absorbs. There are no studies or clinical observations to suggest long
term dangers of Deet when used properly and in accordance with label directions. For straight Deet formulas the EPA publishes absorption rates of up to 20% of the
Deet when alcohol is present, 12% when alcohol is not present. Does the absorption rate of Deet matter if Deet
has been shown to be toxicologically neutral? During periods of heavy repeated use it may be a concern. Continued
presentation of high levels of alcohol-based spray repellents may be irritating to the skin and should be limited.
Composite repellents are absorbed less due to molecule size. Time-release repellents minimize absorption significantly
due to only releasing small amounts of Deet at any one time, rather than flooding the skin with Deet as with straight
Deet applications. |
