• mosquitoes

How to deal with mosquitoes (part 2: DEET)

Last week I talked about how best to treat mosquito bites. I also explained why those annoying pests may find your skin more attractive than your partner’s. I am now going to tell you more about the use of anti-mosquito treatment containing DEET. There is quite some concern about this and I receive lots of questions about it. How safe are those products, and are there alternatives?

Getting straight to the point, I am not a fan of products containing DEET. I would rather not put this substance on my skin. I am, however, a fan of long distance holidays, even to tropical places where dengue fever occurs, where yellow fever, malaria or the zika virus prevails. All of those nasty diseases are spread by mosquitoes. And there isn’t much else to choose from which is as effective as DEET. The advantages of the medicine, in my opinion, then outweigh the possible drawbacks.

Troubling reports

Anti-mosquito sprays and lotions containing DEET remain, worldwide, the most commonly used and most effective treatments against insects which can cause infectious diseases. The substance DEET (N,N-diethyl-meta-toluamide) has been available since the 1950’s. The product was developed in the 1940’s and deployed by the U.S Army for its soldiers. A lot has been done regarding the safety and toxicity of the substance, after a number of disturbing case studies in the late 1980’s about (severe) health complaints in children after using DEET. How does it actually work?

How DEET works

DEET is not a mosquito killer. The substance only prevents mosquitoes from landing on your skin for a blood meal. It isn’t completely clear how this works, but certain receptors in the insects antennae become somehow blocked, making it difficult for them to detect us. It also stops them wanting to bite us.

There are many different treatments containing DEET, with varying concentrations. The concentration of the substance doesn’t so much determine the strength of the treatment, but mainly how long it works for. Sprays and lotions with 10% DEET will provide approximately 3 hours protection, with 15 to 20% this is increased to around 4 to 5 hours and products with 30% DEET work for at least 6 hours.

In areas with the risk of malaria, for example, it is important to choose a product containing a minimum of 30% DEET. Products containing 40%, however, are not recommended due to possible health risks. If you are pregnant or breast feeding then follow the advice about not applying more than 30% of the substance onto your skin. The same applies to children of 2 years of age and under. It is also important with young children that you don’t apply the treatment onto their hands or face, so it doesn’t get into their eyes or mouth. You wouldn’t want that; DEET can be poisonous if swallowed.

Risks and side effects of DEET

In some studies I have read, about the use of DEET, the various described side effects from the past few years were put together in a list. That looks, on first impression, like a disturbing list. From nerve disorders and even convulsions to differing skin complaints and adverse reactions. In most of those cases, oral intake or incorrect (over) use was mentioned.
That is why researchers say that anti-mosquito treatments containing DEET are safe and pose no threat to health with normal and external use as instructed. I, personally think that it would be good if we know more about the long term effects of the substance, and about the actual safe maximum dose.

It is also good that there are increasingly more products being developed with a sealed form of DEET. They last longer on the skin and are less likely to be swallowed.

Be careful with watch straps and your sun cream

But having seen the side effects and health risks caused by DEET many people, including myself, don’t like using the repellents. The smell, the application, the feel it leaves on the skin… And did you know that the stuff can damage things like watch straps and telephones? And, believe me, you wouldn’t want a leaking bottle in your luggage. It can dissolve the lining material in your case, or synthetic fibres in your clothes.

Another disturbing drawback: the effects of your sun creams can be significantly reduced when DEET is applied on your skin. If you want to use both products at the same time, then you need to apply the sun cream first and let it absorb in. I have read in the meantime that a treatment is being developed which protects against both mosquitoes and UV rays.

Alternative and natural substances

Are there any alternatives to DEET? Yes there are. Perhaps you have also looked for one yourself. You will probably have come across names such as icaridin, IR3535 and permethrin then. The first one is no longer for sale in the Netherlands; you can still buy it abroad though. And permethrin is a substance which is mainly used for impregnating things like clothes and mosquito nets, and is also used in anti-lice shampoos.

Alongside this, especially in the last few years, much research has been carried out into natural insect repellent remedies. The most popular and researched are remedies using eucalyptus oil, usually with lemon or lime. Another substance which you will often come across is neem or neem oil (from the Azadirachta indica tree in India).
I, myself, am careful about putting these plant derived ingredients on my skin, which, under the influence of the sun, can also cause aggravating reactions. They are still ultimately less effective against mosquitoes and don’t last as long as the chemical remedies available. And those citronella candles, special citriodiol bracelets and incense are fine, but sadly have little effect. The same goes for electric zappers and vitamin B tablets.

Interesting bacteria

I hope that, in the coming years, the research into our skin microbiome will deliver new insights and fine uses in this area too. In the last blog I mentioned how bacteria and, along with it, body odour plays an important role in the attraction level of the insects. That is why much research is being carried out into manipulating those skin residents. Can you, for instance, alter the composition of your bacteria so that the skin’s odour changes so much that mosquitoes are no longer interested? Can that be done through such things as diet, cosmetics or with probiotics?

The research into this is in full swing, with a view in particular to reducing the enormous numbers of deaths from sicknesses such as malaria. I am confident there will be a lot of new findings from this. I will keep you informed anyway.

Kind regards,


Research Physician Cosmetic Dermatology

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