When bleach and acid mix, toxic chlorine gas usually results. If chlorine gas is created, there is typically a green or brown cloud created in the air.
Avoid mixing bleach and acids such as vinegar or toilet bowl cleaner in the hope of enhancing cleaning power. This combination of substances can lead to significant health problems from the resulting chlorine gas.
Chlorine gas attacks eyes, throat and lungs, and can even cause death with prolonged exposure. Chlorine can also be absorbed by the skin, causing pain and even blistering. Hydrochloric acid, which is created when chlorine gas and water combine, burns skin and can damage internal organs when inhaled.