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DEET – Questions and Answers

DEET is the abbreviation for Diethyl-m-toluamide, or Diethyl-3-methylbenzamide as it is also known. It is a pale yellow, slightly oily liquid at room temperature and it is commonly used as an insect repellent.

It was developed by the United States Army following its experience of jungle warfare during the Second World War. It entered military use as an insect repellent in 1946 and civilian use in 1957.

DEET works as an insect repellent in several different ways:

– it blocks the insect’s olfactory receptors for 1-octen-3-ol, a volatile substance that is contained in human sweat and breath. In other words, it ‘blinds’ the insect’s sense of smell to the presence of humans and makes it difficult for them to find you.

– in addition to blocking some of the olfactory receptors in mosquitoes it also reacts with some of the other receptors in a negative way. In other words, mosquitoes intensely dislike the smell of the chemical and hence it tends to repel them.

It’s very hard to say, because it depends on a number of factors such as the initial concentration, how much you actually put on and how big an area you apply it to, how quickly it is washed off (by rain, sweat or water sports), and even the type of insect! However, the following figures should serve as a rough guide:

– less than 30% DEET – effective for up to 4 hours
– 30 to 50% DEET – effective for 4 to 6 hours
– 50 to 100% DEET – effective for 6 to 8 hours

– It should never really be necessary to use more than 50% DEET, but if you do it is likely that it will remain effective for a bit longer – but not much longer because it will still be washed off or rubbed off over time.

– In particularly wet, humid or strenuous conditions (lots of sweating!) it may be necessary to halve these figures. In general, if you find you’re still being bitten or they’ve started to bite you again – it’s time to apply a bit more.

Generally, DEET works very well with all the insects that are trying to find you so that they can bite you and feed off you – mosquitoes, midges, sand flies, biting flies and fleas, etc. It is also effective against ticks, chiggers and leeches, although it needs to be reapplied more frequently than it does for flying insects to remain effective.

It doesn’t work with spiders and stinging insects – bees, wasps and hornets, etc. Fortunately though these insects don’t usually come looking for you to deliberately bite or sting you – they will only attack if they feel threatened in some way, so the best strategy is try and avoid them and keep out of their way. Similarly, DEET won’t actually repel ants either (because they’re not actively looking for you in the first place) but if they do happen to come into contact with DEET it won’t do them much good!

DEET has been classified by the US authorities as ‘slightly toxic and slightly irratating’ via the eye, dermal and oral routes. It is in Category 3 – the second lowest of 4 categories.

In general – yes – if it is used in accordance with the manufacturer’s instructions. However – as with all chemicals – there will always be a very small minority of people who may react to it in some way. Generally, manufacturers advise that it shouldn’t be used on broken skin and it should be washed off when no longer required. It is said to be suitable for use by anyone over the age of 2, although pregnant mothers and children should use a concentration no higher than 30%.

Generally, manufacturers don’t advise the use of DEET for children under the age of 2. However – if in doubt, consult your doctor. In some areas it may still be preferable on balance to use DEET if there is a serious risk of catching an insect bourne disease. It is generally recommended though that it should never be used on infants less than 6 months old.

In general – yes. Typically the sunscreen should be applied first with the insect repellent on top, so that the sunscreen doesn’t mask the effect of the insect repellent.

Yes and no – DEET is an effective solvent, and hence can ‘dissolve’ some plastics and synthetic materials. It doesn’t dissolve the plastic bottle it’s supplied in but it can harm some other materials. Hence, it should be applied with care, as per the manufacturer’s instructions.

DEET is a moderate chemical pesticide so it may have some effect, but this will diminish very rapidly as it is diluted and it is not thought to bioaccumulate.

Final thoughts:

DEET is used for a reason – to help prevent insect bites. Consequently, the pros and cons should be considered carefully – a milder alternative may be more appropriate in Europe and North America – but it might be foolish to use anything less effective in a high risk area.

DEET can also be used in combination with other measures to increase the overall level of protection – mosquito nets at night time, covering up during the day time with long sleeves and trousers, and treating fabrics with a contact insecticide, such as permethrin.

To shop the range, please see Insect Repellents with DEET.