Olfactory fatigue, also known as odor fatigue, odor habituation, olfactory adaptation, or noseblindness, is the temporary, normal inability to distinguish a particular

odor An odor (American English) or odour ( Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive ...

after a prolonged exposure to that airborne compound. For example, when entering a restaurant initially the odor of food is often perceived as being very strong, but after time passes the awareness of the odor normally fades to the point where the smell is not perceptible or is much weaker. After leaving the area of high odor, the sensitivity is restored with time.

Anosmia Anosmia, also known as smell blindness, is the lack of ability to detect one or more smells. Anosmia may be temporary or permanent. It differs from hyposmia, which is a decreased sensitivity to some or all smells. Anosmia can be categorized int ...

is the permanent loss of the sense of smell, and is different from olfactory fatigue. It is a term commonly used in

wine tasting Wine tasting is the sensory examination and evaluation of wine. While the practice of wine tasting is as ancient as its production, a more formalized methodology has slowly become established from the 14th century onward. Modern, professional w ...

, where one loses the ability to smell and distinguish wine bouquet after sniffing at wine continuously for an extended period of time. The term is also used in the study of

indoor air quality Indoor air quality (IAQ) is the air quality within buildings and Nonbuilding structure, structures. Poor indoor air quality due to indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also be ...

, for example, in the perception of odors from people,

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

, and cleaning agents. Since odor detection may be an indicator that exposure to certain chemicals is occurring, olfactory fatigue can also reduce one's awareness about

chemical hazard Chemical hazards are Hazard, hazards present in Dangerous goods, hazardous chemicals and hazardous materials. Exposure to certain chemicals can cause Acute health hazard, acute or long-term adverse health effects. Chemical hazards are usually cl ...

exposure. Olfactory fatigue is an example of

neural adaptation Neural adaptation or sensory adaptation is a gradual decrease over time in the responsiveness of the sensory system to a constant stimulus. It is usually experienced as a change in the stimulus. For example, if a hand is rested on a table, the t ...

. The body becomes desensitized to stimuli to prevent the overloading of the nervous system, thus allowing it to respond to new stimuli that are 'out of the ordinary'.

Mechanism

Odorants are small molecules present in the environment that bind receptors on the surface of cells called

olfactory receptor neurons An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a sensory neuron within the olfactory system. Structure Humans have between 10 and 20 million olfactory receptor neurons (ORNs). In vertebrates, ORNs are Bi ...

(ORNs). ORNs are present in the olfactory epithelium which lines the nasal cavity and are able to signal due to an internal balance of signal molecules which vary in concentration depending on the presence or absence an odorant. When odorants bind receptors on ORNs, Ca²⁺ ions flood into the cell causing depolarization and signaling to the brain. Increased Ca²⁺ also activates a negative, stabilizing

feedback loop Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...

which lowers the olfactory neuron's sensitivity the longer it is stimulated by an odorant to prevent overstimulation. This happens by limiting the amount of

cyclic AMP Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger, or cellular signal occurring within cells, that is important in many biological processes. cAMP is a derivative of adenosine triph ...

(cAMP) in the cell and by making the Ca²⁺-importing channels which cAMP binds to less responsive to cAMP, both effects reducing further intake of Ca²⁺ and thus limiting depolarization and signaling to the brain. It is important to note that the same mechanism which allows for signaling also limits signaling for prolonged periods of time, the first cannot occur without the second. On the molecular level, as ORNs depolarize in response to an odorant the G-protein mediated second messenger response activates adenylyl cyclase. This increases

(cAMP) concentration inside the ORN, which then opens a cyclic nucleotide gated cation channel. The influx of Ca²⁺ ions through this channel triggers olfactory adaptation immediately because Ca²⁺/calmodulin-dependent protein kinase II or CaMK activation directly represses the opening of cation channels, inactivates adenylyl cyclase, and activates the phosphodiesterase that cleaves cAMP. This series of actions by CaMK desensitizes olfactory receptors to prolonged odorant exposure.

Mitigating scent effects on olfactory fatigue

According to a study by Grosofsky, Haupert and Versteeg, "fragrance sellers often provide coffee beans to their customers as a nasal palate cleanser" to reduce the effects of olfactory adaptation and habituation. In their study, participants sniffed coffee beans, lemon slices, or plain air. Participants then indicated which of four presented fragrances had not been previously smelled. The results indicated that coffee beans did not yield better performance than lemon slices or air.

References

External links

* {{Cite journal , vauthors=Kristensen HK, Zilstorff-Pedersen K , date=December 1953 , title=Quantitative studies on the function of smell , journal=Acta Oto-Laryngologica , volume=43 , issue=6 , pages=537–44 , doi=10.3109/00016485309119884 , pmid=13138121 Building biology fatigue, olfactory Wine tasting Indoor air pollution

Mechanism

Mitigating scent effects on olfactory fatigue

See also

References

External links