A review published in 2010 looked at adverse events associated with N,N-diethyl-m-toluamide (DEET) listed in the DEET Registry, a post-marketing surveillance system designed to monitor patterns of medical events tied temporally to the product. Between 1995 and 2001, Osimitz et al (2010) noted 296 moderate and major severity cases include in the registry, with 14.5% of these considered to probably be related to DEET exposure, and 65% of cases possibly due to exposure. The rest (20.2%) had too little information to make an assessment.
Dangers of DEET in Children
Nearly half of all cases were reported in children nineteen years old or younger. Seizures were experienced in 42% of children and a wide variety of other neurological issues were also recorded. The plethora of neurological symptoms makes many sceptical of condemning DEET as the causative factor as it is unlikely that a single agent has such a varied impact. Another finding of the registry analysis was that those with underlying neurological problems, or those on medications were not more likely to report adverse events occurring with DEET use. Additionally, the concentration of DEET appeared unrelated to the reports of adverse effects. The authors’ note that the low incidence of neurological symptoms reportedly associated with DEET, and the lack of clear causation between the two make the product appear relatively safe given its widespread use in the US by both adults and children.
DEET and Neurological Disease
However, an earlier study, by Corbel (et al, 2009), found evidence of a negative effect of DEET on cholinesterases in insect and mammalian nervous systems. These French researchers focused their attention on the interaction between DEET and carbamate insecticides on the cholinergic system and found that DEET did indeed have the potential to increase the toxicity of carbamates, a group of insecticides already known to block acetlycholinesterase, thus giving rise to potential neurological damage. Diseases such as Alzheimer’s, Parkinson’s, and myasthenia gravis, are all connected to dysfunction of acetylcholine in the nervous system, along with numerous other neurological and neuromuscular diseases. The connection between DEET and neurological damage has led some states to restrict the concentrations in which it is available, although it does appear that it is the interaction between DEET and other insecticides that presents the danger to nervous system function.
Learning About Tick Repellents
The ubiquity of DEET makes it important that the general public knows of the possibly harmful interactions between different chemicals used as insecticides. Unfortunately, little is done in terms of specific education on such matters. Legislation changes in recent years have however resulted in labelling guidelines intended to protect specific populations from overexposure to DEET, such as children, and infants.
DEET Exposure in Infants and Children
Most reported adverse events related to DEET occur as skin reactions from products with a high concentration of the chemical (50% of more). Children more commonly suffer adverse effects of DEET and there have been cases of slurred speech, confusion, seizures, and even coma and death. Most exposure is through the skin, but some hazardous exposure to DEET can occur through inhalation or ingestion of the product. As such, children should not be allowed to apply the insect-repellent themselves and the amounts used should be minimized as far as possible.
There are a number of alternatives to using DEET and permethrin, with a small number of researchers looking into natural compounds that act as acaracides. The effectiveness of DEET against ticks is questionable, despite its efficacy against mosquitoes, making it more likely that people turn to permethrin or other chemicals to combat Lyme disease. In the meantime, it is important that any adverse events related to DEET and permethrin are reported so that a clearer picture of their impact can be obtained.
Osimitz TG, Murphy JV, Fell LA, Page B, Adverse events associated with the use of insect repellents containing N,N-diethyl-m-toluamide (DEET). Regul Toxicol Pharmacol. 2010 Feb;56(1):93-9. Epub 2009 Sep 12.
Corbel V, Stankiewicz M, Pennetier C, Fournier D, Stojan J, Girard E, Dimitrov M, Molgó J, Hougard JM, Lapied B., Evidence for inhibition of cholinesterases in insect and mammalian nervous systems by the insect repellent deet. BMC Biol. 2009 Aug 5;7:47.