Insect Repellents

We often tell people that the most dangerous wild animal in Africa is the mosquito.  Actually, this is true in many other parts of the world as well. 

A host of diseases are spread by insects.  Probably the most well known of these is malaria.  Other diseases for which the mosquito is the carrier include yellow fever, dengue fever, Japanese encephalitis and West Nile virus.  Tsetse flies spread African sleeping sickness, reduuvid beetles infect you with Chagas disease, sand flies carry leishmaniasis and ticks are responsible for Lyme disease, typhus and several other diseases.  As you can see, it’s a jungle out there!

We are often asked, therefore, what insect repellents are effective and how safe they are to use in pregnancy.

The bottom line is that careful medical studies have shown only two substances to be effective in this regard.  These are N, N-diethyl-m-toluamide (DEET) and a new substance named Picardin.  Other substances such as citronella may repel insects for a few minutes, but not long enough to be of use for medical protection.

Significantly not effective in medical studies are commonly touted remedies such as consuming large amounts of vitamin B or slathering oneself with various cosmetic preparations.

DEET has now been around for over 50 years and is the active ingredient in almost all commercial insect repellents.  Concentrations vary from 5% to 100%, depending on the brand one buys.  Any concentration of DEET is an effective insect repellent, but historically it has been a matter of the higher the concentration, the longer the duration of its effectiveness.  Thus, people going to the Amazon have been advised to use 100% solutions that will last all day.  Unfortunately, this strength will also irritate the skin and even melt your watch crystal and eyeglass lenses.

Recently two controlled-release formulations have become available (Sawyer Controlled-Release® and Ultrathon®) that have a lower concentration of DEET but last all day and don't disappear if you sweat or go swimming.  Most evidence suggests that these are as effective as and much less irritating than the higher concentration products.

It should be remembered that DEET is not as effective in repelling lice, ticks and tsetse flies as it is for mosquitoes.  It is more effective than anything else, however, and we still recommend its use.  For these insects, combining DEET with Permethrin works best (see below.)

Over the years, there have been reports of serious side effects with DEET.  There were some cases, for instance, of seizures in small children.  But these were instances where the children were doused head to foot in large amounts of the substance, far beyond recommended dosage.  Similarly, a report of neurological problems in a baby born to a woman using DEET was in a patient who used large amounts daily throughout the pregnancy and was also taking other medicines that could have been responsible for the problem.  Otherwise there have been no reports of problems with its use in pregnancy.

A recent study, published in the Journal of Travel Medicine, showed DEET to be effective and perfectly safe in concentrations of up to 20% in pregnant women in their second and third trimester.  A later report, using higher concentrations and including use in the first trimester is expected in the near future.

At this point, Picardin has not been around long enough for us to comment on its safety in pregnancy.  Experience with the product is rapidly increasing in Europe, however, and we should have further news soon regarding its use in pregnancy.

Although an insecticide rather than an insect repellent, another commonly recommended product is Permethrin®, containing a chemical called pyrethrin and made from a flower called Pyrethrium.  This product is sprayed on clothing, mosquito nets and bedding and effectively kills over 100 kinds of insects.  Despite its effectiveness, it is non-irritating to the skin and appears perfectly safe in pregnancy.  It is an excellent additive to the protection afforded by insect repellents.