The allethrins are a group of related synthetic compounds used in insecticides. They are synthetic pyrethroids, a synthetic form of a chemical found naturally in the chrysanthemum flower. They were first synthesized in the United States by Milton S. Schechter in 1949. Allethrin was the first pyrethroid. If a chemical ends in -thrin it is unlikely to kill mites or help in any significant way. These chemicals are more likely to harm you than harm mites.