Science Questions with Surprising Answers
Answers provided by
Dr. Christopher S. Baird

How strong does a non-toxic odor have to be before it damages your sense of smell?

Category: Biology      Published: June 10, 2014

woman smelling strawberry
Public Domain Image, source: National Cancer Institute.

The sense of smell does not really work that way. If an odor, such as the smell of a strawberry, is not chemically reactive enough to do damage, your sense of smell will remain unharmed no matter how strong the smell becomes. In this way, the sense of smell is very different from the sense of sight and the sense of hearing.

The brightness of a light is a measure of its energy content. A brighter beam of light carries more energy. Therefore, light can be bright enough that it dumps enough energy into your eyes to damage them. Similarly, the loudness of a sound is a measure of its energy content. A louder sound carries more energy. In this way, sound can be loud enough to dump enough energy into your ears to cause damage. In contrast, the strength of a particular odor is not a measure of its energy content, but is a measure of the number of odor molecules in a given volume. A stronger concentration of a particular order that reaches your nose is not dumping more energy in your nose. It is dumping more odor molecules in your nose. Your nose contains an array of smell receptors (olfactory nerves). When the odor molecules bind to these smell receptors, they trigger a signal to the brain telling it that something was smelled. The more odor molecules there are present, the more binding there is to the smell receptors, and the stronger the smell signal that reaches your brain.

If a particular non-toxic odor is too strong, this just means that it carries too many odor molecules for your sense receptors to bind to, and not that it is dumping too much energy into your nose. Therefore, if a particular odor is not toxic, it will do no damage no matter how strong the smell becomes. If the smell of bacon gets too strong, you simply stop noticing that the smell is getting stronger because your sense receptors are saturated, but no damage is done and no pain is felt.

Odors that are chemically reactive enough will affect your sense receptors at any concentration. At low concentrations, the effect is minimal. At higher concentrations, the inhaled toxic chemical can lead to nasal irritation, long-term damage, and even cancer. For example, hydogen sulfide gives a recognizable rotten-egg smell at a concentration of about 5 parts per billion, becomes annoying at about 100 parts per billion, causes irritation at about 10,000 parts per billion, and causes lasting damage and even death at higher concentrations.

In the textbook Taste and Smell Disorders edited by Allen M. Seiden, the authors Lloyd Hastings and Marian L. Miller write, "Among the many causes leading to decrements in olfactory function, exposure to toxic compounds, especially those airborne, represents a small but important percentage of the cases presenting for evaluation...Exposure to levels of irritants sufficient to alter olfactory function usually occurs only after accidental exposure."

Topics: odor, saturation, smell, toxic