Picaridin (
pih-CARE-a-den)
Bayer AG came up with picaridin in 1980, but it didn't start to hit shelves until 1998 around the world and in 2005 in the US. Picaridin is a derivative of the plant genus Piper and a less but still "moderately toxic" compound for rainbow trout. The EPA's recent research suggests that it's as effective against ticks as DEET, and on average, lasts longer. The EPA, CDC, and WHO all agree that it's a comparable DEET alternative.
The compound is more popular in Australia and Europe, where it has been available since 1998 and tick-borne illnesses are slightly less common, but DEET remains the staple in the United States.
DEET
Developed by the US Army to protect soldiers from tropical disease-bearing insects in the tropics, DEET or N,N-Diethyl-m-toluamide has been the most popular bug repellent in the US since it hit the mass market in 1957. While there has been some degree of controversy over its toxicity, it is highly effective at warding off ticks, mosquitos, and ot ehr insects.
Scientific research published this year by the CDC (Center for Disease Control) shows that of the 650,000 cases of vector-borne (blood-feeding insect-originated) diseases reported in the United States over a 12-year period from 2004-2016, more than 75% were from ticks. So while DEET may be less than ideal for aquatic creatures, it is great protection against the serious diseases you can get from ticks, mosquitos, and so on. The real issue with DEET is that it's highly toxic to aquatic creatures.
Permethrin
A synthetic derivative of the chrysanthemum flower, permethrin is an insecticide used to exterminate mites like lice and scabies, but it's also effective with anything else, which is why the US Army has been treating BDU's with it for the last two decades.
Permethrin is perhaps the least toxic of all the chemical-based bug repellents, but it's also the most odorless and the least effective on bare skin, where it can wear off in as quickly as 15 minutes. On the other hand, it lasts many weeks when applied to clothing — even after several washes — and because it's odorless, it's the ideal bug spray for hunters, anglers, and wildlife stalkers.
IR3535
In the 1970s, Merck developed something called IR3535, which stands for "Insect Repellent 3535," and could probably stand to take on a common name. It was only introduced to the mass market in 1999 and is billed by the EWG as being a "strong" mosquito repellent, and a "good" tick repellent, which isn't quite good enough to knock DEET or picaridin off their thrones, at least at this point.
Essential oils
While not exactly clinically proven, a combination of essential oils is endorsed by many, and, as someone who spends countless hours in tick-infested wooded and shrub-strewn areas, I haven't found a tick on myself since I started using them, particularly the formula put together by Burt's Bees, which also, in my opinion, smells kind of nice, too. I also like that you can rub them all over your face without worrying about ingestion.