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From: (Steven B. Harris )
Subject: Re: 13yr old exposed to DEET
Date: 24 Jul 1995

In <3uvaig$> (Douglas Rockwell)

>Are you sure he didn't get bitten by a tick in spite of the DEET and is
>actually suffering from Lyme disease?
>DEET has been used by millions of people for over 50 years; if it were
>even uncommonly toxic it seems like we would know about it by now (but
>come to think of it, I saw a teaser for a tabloid TV show that said
>something about bug repellents being harmful to humans...).
>best wishes

I had the same thought.  DEET isn't even harmful to mosquitos.  It's
just slimey and the little buggers hate the feel of it on their little
foot hairs.  Also it keeps them from getting a grip-- I've seen them
land and literally roll off an arm (hilarious).  Any 13 year old with
CF should get worked up for something else.  There's also a psych
component not to be missed: CF is so rare in 13 year olds, that I'd
also look for somebody else in the family who has it. Children learn
from adults.

                                     Steve Harris, M.D.

Subject: Re: BUG SPRAYS: Which are best?
From: (Lee Albert Green MD MPH) 
Date: Jul 13 1995

Matt Haws ( wrote:
: I am posting this to see if anyone out there might be able to direct me to a 
: brand of bug repellant that works best while riding. I live in northern 
: Indiana and ride frequently on my trial in my woods. The only problem is the 

Brand makes little difference.  There's good research on insect 
repellants, so with all due respect to the many and varied firmly held 
opinions of outdoorspeople everywhere, I'll share the cold hard data.

Nothing will prevent all bites except barriers (e.g., netting and 
bug suits).  There is NO, repeat NO, perfect repellant.

Avon Skin-So-Soft really does work, in that it reduces bite frequency per 
hour compared to placebo (plain skin lotion).  It's not stupendously 
effective, reducing bite frequency by about 60%, but it's very safe and 
in low-bug-density situations 60% reduction may be enough.

DEET (n,n-diethyl meta-toluamide) is a derivative of toluene, an organic 
solvent, and is the most effective biting-insect repellant yet 
discovered.  It's a great solvent, cheerfully eating polystyrene foam 
(like your helmet), stripping paint, and generally doing all the other 
things you can do with toluene.  It will take the bugs off your 
windshield very well, BTW.  It will ruin your Oakleys INSTANTLY and 
irreparably on contact.

How well DEET works depends on the concentration in which it's applied.  
Low-strength stuff like Off!, 12.5% DEET, is 60-75% effective.  100% DEET 
can be 95%+ effective for over 4 hours on blackflies (Simulium spp.) and 
up to 10-12 hours on mosquitos of all three major genera (Anopheles, 
Culex, and I never remember the tiger mosquitoes' genus name).  It's fair 
to middling effective on ticks, very effective on chiggers, punkies, and 
no-see-ums.  Actually though 100% DEET is more marketing than science; it 
sounds strong, but the most effective DEET-only formulation is 70% DEET 
in ethanol.  That's 98% effective for 10 hours.  It's sold as Safesport, 
familiar to Vietnam vets in its clear US Army issue bottle but sold in OD 
bottles now.  I personally use 50% DEET (Cutter, Repel, whatever; brand 
doesn't matter) as a nice compromise, unless I'm going into wetlands 
during the nastiest season.  Then I break out the Army surplus stuff.

The most effective DEET formulation though is the 50% DEET in ethanol 
with musk.  Musk is used by perfume makers to increase the duration of 
their perfumes' persistence.  It works for DEET too.  If you can find it 
it's great.  It also costs!

Is DEET safe?  Low concentrations certainly are OK.  High concentrations 
applied to large skin areas can lead to significant blood levels though, 
which can cause seizures in rare cases.  There's no evidence it causes 
cancer, kids with three heads, or any other scare stories.  If the bugs 
are thick, I wear long pants and sleeves, and use the strong stuff on the 
small areas remaining.  If I'm going to DEET large areas of legs and 
arms, I use 25%, or 50% tops.  The kids never get more than 25% except on 
small exposed areas, when they get 50%.  DON'T get it in your eye, it can 
destroy your cornea.

For ticks, permethrins are more effective than DEET.  There are 
repellants on the market which combine the two, but I don't know of any 
permethrin-only repellants.  Permethrins are quite safe.  They don't 
impress skeeters or blackflies at all.

There are still some scarce repellants which use n-hexanol, an alcohol.  
It's about as effective as skin-so-soft, with little evidence of toxicity.

No repellants are particularly effective against deerflies.  Many people 
confuse deerflies with blackflies; blackflies are quite small though 
(4-6mm long), whereas deerflies are about the size of houseflies.

Hope that treatise helps -Lee

Lee Green MD MPH
Dept Family Practice
University of Michigan

Version: 2.6


From: Steve Harris <>
Subject: Re: DEET Products Questions
Date: 4 Jul 2005 14:20:34 -0700
Message-ID: <>

>>Have a friend who is lactose intolerant, and as a result apparently emits a
higher level of CO2 than most folks while exhaling. <<


LOL. Unless you see mosquitos congregate in the region of his anus, I
don't think you blame lactose intolerance.

Mosquitos sense CO2 and a wide variety of other chemicals. But the
amount of CO2 you make from normal energy metabolism is gigantic and
unchangable, except by things which slow your metabolic rate (like
holding still and keeping warm so you don't shiver). It's easy to keep
warm, but holding still just makes you a better mosquito target. Forget
about CO2.

DEET acts by blocking a variety of receptors on mosquito antennae.
Picaridin products work probably the same way, and is another repellent
recently recommended by the CDC. Lemon eucalyptus oil also works, and
David Wright indicates, but we don't know how.

DEET is still the best of the scientifically tested repellents. DEET
safety issues remain, but mostly in pediatric use.

J Med Entomol. 2004 May;41(3):414-7.

Field evaluation of repellent formulations containing deet and picaridin
against mosquitoes in Northern Territory, Australia.

Frances SP, Waterson DG, Beebe NW, Cooper RD.

Australian Army Malaria Institute, Gallipoli Barracks, Enoggera,

Field efficacy of repellent formulations containing picaridin
(1-methyl-propyl 2-(2-hydroxyethyl)-1-piperidinecarboxylate) or deet
(N,N,-diethyl-3-methylbenzamide) against mosquitoes in Northern
Territory, Australia, was evaluated. The following repellent treatments
were evaluated:  19.2% picaridin (Autan Repel Army 20), a solution of 20%
deet in ethanol, and 35% deet in a gel (Australian Defense Force [ADF]).
The predominant mosquito species were Culex annulirostris Skuse (57.8%),
Anopheles merankensis Venhuis (15.4%), and Anopheles bancroftii Giles
(13.2%). The protection provided by repellents against Anopheles spp. was
relatively poor, with 19.2% picaridin and ADF deet providing >95%
protection for only 1 h, whereas 20% deet provided <95% protection at 1 h
after repellent application. In contrast, the repellents provided good
protection against Cx. annulirostris, with 19.2% picaridin providing >95%
protection for 5 h and both deet formulations providing >95% protection
for 7 h when collections ceased. This study provides additional field
data showing tolerance of Anopheles spp. for repellents. The response of
field populations of Cx. annulirostris, an important vector of
arboviruses in Australia, to repellents containing deet and picaridin is
reported for the first time.

PMID: 15185943 [PubMed - indexed for MEDLINE]

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