Icaridin, also known as picaridin, is an insect repellent which can be used directly on skin or clothing. It has broad efficacy against various insects and ticks and is almost colorless and odorless. The name picaridin was proposed as an International Nonproprietary Name to the World Health Organization, but the official name that has been approved by the WHO is icaridin. The chemical is part of the piperidine family, along with many pharmaceuticals and alkaloids such as piperine, which gives black pepper its spicy taste. Trade names include Bayrepel and Saltidin among others. The compound was developed by the German chemical companyBayer and was given the name Bayrepel. In 2005, Lanxess AG and its subsidiary Saltigo GmbH were spun off from Bayer and the product was renamed Saltidin in 2008.
Effectiveness
Icaridin has been reported to be as effective as DEET without the irritation associated with DEET. According to the WHO, icaridin “demonstrates excellent repellent properties comparable to, and often superior to, those of the standard DEET.” In the United States, the Centers for Disease Control and Prevention recommends using repellents based on icaridin, DEET, ethyl butylacetylaminopropionate, or oil of lemon eucalyptus for effective protection against mosquitoes that carry the West Nile virus, Eastern Equine Encephalitis and other illnesses. Icaridin does not dissolve plastics. Icaridin-based products, first used in Europe in 2001, have been evaluated by Consumer Reports in 2016 as among the most effective insect repellents when used at a 20% concentration. Icaridin was earlier reported to be effective by Consumer Reports and the Australian Army. Consumer Reports retests in 2006 gave as result that a 7% solution of icaridin offered little or no protection against Aedes mosquitoes and a protection time of about 2.5 hours against Culex, while a 15% solution was good for about one hour against Aedes and 4.8 hours against Culex.
Larval salamander toxicity
A 2018 study found that icaridin, in what the authors described as conservative exposure doses, is highly toxic to salamander larvae. The study observed high larval salamander mortality occurring delayed after the four days of exposure. Because the widely used LC50 test for assessing a chemical's environmental toxicity is based on mortality within four days, icaridin would be incorrectly deemed as "safe" under the test protocol.
Chemistry
Icaridin contains two stereocenters: one where the hydroxyethyl chain attaches to the ring, and one where the sec-butyl attaches to the oxygen of the carbamate. The commercial material contains a mixture of all four stereoisomers.
Commercial products containing icaridin include Cutter Advanced, Skin So Soft Bug Guard Plus, Autan, Smidge, PiActive and MOK.O.
Mechanism
A potential odorant receptor for Ιcaridin, the CquiOR136•CquiOrco, has been suggested recently for Culex quinquefasciatus mosquito. Recent crystal and solution studies showed that Icaridin binds to Anopheles gambiaeodorant binding protein 1. The crystal structure of AgamOBP1•Icaridin complex revealed that Icaridin binds to the DEET-binding site in two distinct orientations and also to a second binding site located at the C-terminal region of the AgamOBP1. Recent evidence with Anopheles gambiae mosquitoes suggests icaridin does not strongly activate olfactory receptors neurons, but instead functions to reduce the volatility of the odorants to which it is mixed. By reducing odor volatility, icaridin functions to "mask" the ability of volatile odorants on the skin to activate olfactory neurons and attract mosquitoes.
