irritant
fog is made up of water and smoke is a irratant or gas.
Butylphenyl methylpropinal is a man-made substance commonly used in beauty products. It has been found to be irratant to the skin if used in high concentrates and can cause sperm damage.
Poison Ivy is poisonous because it contains a chemical called Urushiol that acts as a protectant to help keep the plant from being eaten. It just so happens that the Urushiol is an extreme irratant, to not only those that may try to eat the plant, but also to other things as well.