Mixing household chemicals, particularly cleaners, can produce toxic or even deadly fumes. You may be aware you should never mix bleach and ammonia or bleach and vinegar, yet might not realize trying to boost the cleaning power of detergent or toilet bowl cleaner is similarly dangerous. Sulfide salts or solutions react with acids to form hydrogen sulfide gas (H2S, shown). This is the chemical responsible for the rotten-egg smell, but exposure to hydrogen sulfide eventually deadens the sense of smell and can kill you. The gas is heavier than air, so it can settle toward the ground or find its way down stairs. If you smell the rotten egg odor when chemicals are mixed, it's a good idea to call 911 rather than just air out the room and return later because the gas could pose a threat to your family, pets and neighbors.
Mixing toilet bowl cleaner and bath salts or detergent and bath salts has been used as a suicide method in Japan and the UK. Readers should be aware this is a particularly selfish way to poison one's self, since the gas has the potential to harm rescue workers and innocent bystanders.