Hydrogen sulfide is a colorless gas known for its distinct smell, often compared to that of rotten eggs. It is produced naturally by the breakdown of organic matter and can be found in places like swamps, volcanic gases, and even in some industrial processes. This gas is highly toxic and can be dangerous in high concentrations, leading to health issues or even death. Safety measures are essential when working in environments where hydrogen sulfide may be present, such as sewage treatment plants or oil refineries.