Seresto by Elanco (formerly Bayer Animal Health) is a collar for cats and dogs that provides long-lasting antiparasitic protection through the gradual release of imidacloprid and flumethrin onto the animal's skin. Although the EPA has deemed Seresto safe, their assessment is based on laboratory data, which may not fully reflect real-world exposure. Furthermore, recent reports of over 900 adverse human health events between 2012 and 2022 underscore the need for further safety investigations. We measured these chemicals' concentrations from the fur of eight dogs over 9 months to evaluate how daily interactions with pets could expose humans to toxic levels. Flumethrin was mostly undetectable, and imidacloprid levels were well below the toxicity threshold, suggesting low risks. However, factors like cumulative exposure and individual characteristics warrant consideration. Concentration levels were highest right after collar application, potentially reaching up to 11.6% of an 8 kg child's acceptable daily intake. We recommend limiting prolonged contact with pets, especially for young children, in the first 48 h post-application. We detected residual imidacloprid prior to collar application and 1 month after removal, raising questions as to the potential contamination risks that roaming pets could pose to ecosystems, given the known environmental impacts of these chemicals.