No Listerine for you then?
Poison is a term relative to whether it is ingested or not. Some things that are toxic are totally fine on your skin but can't be breathed in. Some things can't be breathed in but if they're ingested are fine.
Our bodies handle chemicals pretty strangely. It is all extremely dependent on the circumstance, amount of the chemical, etc.
For instance, think of Chlorine. We swim in pools with tons of Chlorine dumped in them all the time. Do you like to jump in big vats of a toxic chemical mixed with water?