The study showed that cancer development was unrelated to cigarette smoke and household chemicals, but an increased risk occurred with topical insecticide use. (bracpet.com)
Once a month topical insecticides like Advantix, Frontline, and Spot On are some pretty effective examples. (blog.pawedin.com)
Perhaps they combined products, like the older insecticide - laced flea collars with other topical insecticide products. (2ndchance.info)