Actually, that's not true, SV. For example, never burn poison ivy, as the fumes can be very dangerous to your lungs if inhaled. The other is that the oil can survive a long time, so if you touch something that has the oil on it, you can get it, even if you've never left the house.

For example, if your dog rubbed against some and you then pet your dog, you can get it. If someone was working in the garden and got the oil on their clothes, and you now touch those same clothes, you can get it.