Pyrethrins have been used for more than 100 years and take aim at the nervous system of ticks by causing repetitious rapid nerve impulses, resulting in death. They are naturally occurring chemicals, extracted from chrysanthemum flowers, and are not limited to tick control. Pyrethrins also can be used to control fleas, lice, some mites, and mosquitoes. Because they have a low toxicity, pyrethrins are used in products that can be applied directly to the pet’s skin. You can find pyrethrins as active ingredients in shampoos, dips, powders, and spray formulations.