Never mix toilet bowl cleaner with bleach because a toxic gas could be released. Hazardous fumes pose several serious health hazards that could even result in death if the concentration of the resultant gases is high enough.
The active ingredient in bleach is chlorine. The active ingredient in toilet bowl cleaner is hydrochloric acid.
Mixing chlorine and acid immediately produces a deadly chlorine gas. This chemical reaction can prove deadly.
Breathing chlorine gas poses moderate to severe health risks. Corrosive chlorine gas irritates the eyes, nose and throat, causing burning and breathing difficulties. Severe reactions to high concentrations of chlorine gas include chest pain, vomiting, profound breathing problems and death.
It is critical to always follow warnings on household chemicals and cleaning products. If mixing of toilet bowl cleaner and bleach occurs, immediately open the windows and get fresh air. Immediately leave the affected area until it can safely be ventilated adequately so that the gas completely dissipates.
To avoid the health hazards associated with household chemical-based cleaners, consider using safer cleaners that do not contain bleach or acid. If choosing to continue cleaning with bleach- or acid-based cleaners, use only one type to avoid accidental mixing.