Hydrogen sulfide

One of the most foul-smelling substances is hydrogen sulfide (H 2 S), which has a characteristic rotten-egg odor. This gas is produced by the anaerobic (oxygen-free) breakdown of organic matter by bacteria; it is a common component of “sewer gas.” But this gas does not cause disease; rather, when molecules of this substance enter your nose, they can attack the central nervous system. Exposure to even small amounts can be fatal.

The health effects of hydrogen sulfide depend on the amount inhaled and for how long. Exposure to low concentrations (less than 50 parts per million (ppm)) can produce irritation of the nose and throat and lead to loss of appetite and headache. Higher concentrations (50–150 ppm) can cause eye irritation, coughing, and loss of smell. If the amount of inhaled hydrogen sulfide is larger than 200 ppm, damage to the eyes can occur, along with accumulation of fluid in the lungs. Beyond 700 ppm, most people lose consciousness, and some die.

The bottom line…

Your sense of smell often alerts you to potential danger. Bad smells can serve as a warning that something is amiss. If it smells bad, it is probably bad for you. More often than not, the nose knows.

What’s that smell?

Thinking of a recent or past experience with a bad smell, what chemicals do you think caused that bad smell? Do you think they were harmful? How would you find out?