Due to the targeted chemical modification, pyrethroids are more stable and more long-lasting in their effectiveness than natural pyrethrum. This sounds positive at first, but: Due to their longevity, pyrethroids can enter the body of mammals, even if only in small quantities. They can be absorbed through breathing, the skin or food. When used as a spray, the toxins are absorbed directly through the lungs into the bloodstream. There are therefore restrictions on the use of pyrethroids, particularly in cats, as they are less able to break them down than other animal species. Cats are also particularly susceptible to pyrethroid poisoning, which is usually fatal. However, some side effects can also occur in humans.