http://www.epa.gov/oppsrrd1/REDs/fa...n_fs.htm#health
the Agency classified permethrin as “Likely to be Carcinogenic to Humans” by the oral route. This classification was based on two reproducible benign tumor types (lung and liver) in the mouse, equivocal evidence of carcinogenicity in Long- Evans rats, and supporting structural activity relationship information.

這篇 EPA 說是要經由口服。