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Evidence for dangers of repellent DEET in question

The benefits of avoiding disease-spreading insect bites outweighs the potential risks of using DEET, according to a review of the evidence in the open access journal Parasites and Vectors.

The review looked at a range of studies on the safety of using DEET, including animal research, case reports and other safety assessments, and reached the conclusion that there is no evidence of severe adverse events associated with recommended DEET use.

The authors say that it is important for holidaymakers to protect themselves from the risks of tropical disease by preventing insect bites in the first place, using effective repellents like DEET. This paper is published to coincide with the launch of Bug off – an Insect Repellent Awareness Day.

Dr James Logan, Director of arctec at the London School of Hygiene & Tropical Medicine says: “If DEET products are restricted to just 15%, it is likely that millions of people will be put at greater risk of mosquito bites which will dramatically increase their likelihood of developing a disease like malaria or dengue as a result. There is plenty of evidence to show that low levels of DEET are not very effective, so it is important that travellers have access to repellents with greater levels of DEET that will provide the best protection.”

DEET is an abbreviation for N,N-diethyl-m-toluamide, which was developed by the US army for jungle warfare just after World War II. It’s now the active ingredient in many commercial topical repellents, and is widely accepted by scientists as the most effective known repellent to prevent insect bites which can transmit dangerous diseases like malaria and dengue. However, some governments limit the concentration of DEET in repellents, due to safety concerns after reports of encephalopathy (brain disease) following DEET use.

The researchers reviewed the scientific evidence on the safety of DEET use and found that there was insufficient evidence for risks in humans. Their search discovered only one existing human trial on the safety of DEET, in pregnant women in Thailand. This study compared women who used a DEET-based repellent to prevent malaria transmission to a control group. There was evidence of traces of DEET in the children, suggesting that the substance could cross the placental barrier, but, crucially, no differences in the health of the babies between the DEET treatment group and the control group babies.

The review also looked at existing animal studies to assess the safest amount of DEET to use in repellents and found that insufficient evidence had been gained from these to justify any imposed limits on concentration of DEET. Based on this, the authors weigh the safety risks found in trials against the protection that DEET-based repellents give against transmission of diseases.

Dr Logan says: “Our review article found very few studies that suggested any adverse effect of DEET. In fact, there were only 14 cases of encephalopathy associated with DEET which is extremely small considering the estimated 200 million applications of DEET to the skin each year. If DEET caused serious health problems, we would know about it by now.”


Assessment of methods used to determine the safety of the topical insect repellent N,N-diethyl-m-toluamide (DEET): a critical review, Vanessa Chen-Hussey, Ron Behrens and James G Logan,Parasites & Vectors, DOI:10.1186/1756-3305-7-173, published online 3 June 2014.

BioMed Central