How smell works
First, let’s see how we
smell things. Smell is due
to molecules of a particular substance that
travel into your nose.
These odor molecules
contact a tissue called
the olfactory epithelium
(Fig. 1), which contains
olfactory receptor cells
that lock onto these odor
molecules. This generates electrical signals
that are relayed to clusters of nerve cells called
glomeruli. Then, specialized nerve cells called
mitral cells send these signals to regions of the brain that will
combine these signals so we can recognize the smell (or are
intrigued by it).
Smell does not usually contain bacteria, which carry disease and are much larger than the gaseous molecules that
make up a smell. So the odor itself cannot make you sick.
But some gaseous compounds can have other effects
on your health by causing shortness of breath, headaches, eye irritation, or, if large amounts are inhaled,
One of the most foul-smelling substances is hydrogen
sulfide (H2S), 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 com-
Can Smells Harm You?
Can smells be bad for you? Most of us recall situations where a pungent odor—say, from a sewer, trash sitting outside, or a dirty
public bathroom with a strong odor of urine—made us want to run away.
“Run for your life!” you may have said to yourself. Other times, the air in
a friend’s house living room was so stuffy you had difficulty breathing,
or the air in your classroom smelled like dirty socks, and there were no
windows to let fresh air in. Were you going to get sick?
ponent of “sewer gas.”
Hydrogen sulfide is quite
toxic, and exposure to
even small amounts can
The health effects
of hydrogen sulfide
depend on the amount
inhaled and for how
long. Exposure to low
than 50 parts per million
(ppm)) can produce irritation of the nose and throat
and lead to loss of appetite and headache. Higher
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?
www.acs.org/chemmatters 4 ChemMatters | APRIL/MAY 2016
Figure 1. When you smell a smelly substance, odor molecules travel to
your nose, where they bind to olfactory receptor cells ( 6), which generate
electrical signals that are sent to a part of your brain called the olfactory
bulb (1). Also shown are mitral cells ( 2), bone ( 3); olfactory epithelium (4),
and glomerulus ( 5). See the text for more details.
By Brian Rohrig