Hydrogen sulfide is a toxic gas that acts as a cellular asphyxiant, similar to cyanide, and has a strong odor of rotten eggs. Hydrogen sulfide has some industrial uses and is naturally occurring in the environment as a byproduct of decomposing organic matter, sewage, sulfur springs, and natural gas.

Low exposures to hydrogen sulfide produce skin irritation and redness, nasal pain, sore throat, eye pain, lacrimation, blepharospasm, tracheobronchitis, pneumonitis, and pulmonary hemorrhage with hemoptysis.

Moderate exposure may also produce sudden onset of rapid, gasping breaths, tachycardia, flushing, headache, and dizziness followed by nausea, vomiting, confusion, agitation, cyanosis, and coma.

High exposure will produce several seconds of rapid, gasping breaths quickly followed by apnea, seizures, coma, and death from respiratory arrest. Skin, mucosal, and airway symptoms usually do not have time to manifest themselves.