Dysosmia, also known as olfactory dysfunction, is the impairment of olfactory stimuli processing leading to an altered sense of smell

Smell

Smell may refer to:* Olfaction, sense of smell, the ability of humans and other animals to perceive odors* Odor, the percept resultant from the sense of smell...

.

These dysfunctions can present in a variety of ways, such as the stimuli not activating the olfactory bulb

Olfactory bulb

The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...

, some odors being interpreted as other odors, or hallucination

Hallucination

A hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid,...

s of smells. These subsets are called anosmia

Anosmia

Anosmia is a lack of functioning olfaction, or in other words, an inability to perceive odors. Anosmia may be either temporary or permanent. A related term, hyposmia, refers to a decreased ability to smell, while hyperosmia refers to an increased ability to smell. Some people may be anosmic for one...

, parosmia

Parosmia

Parosmia, also known as troposmia or cacosmia, is an olfactory dysfunction that is characterized by the inability of the brain to properly identify an odor’s “natural” smell....

, and phantosmia

Phantosmia

Phantosmia, or olfactory hallucinations, involves smelling odors that are not derived from any physical stimulus. These phantom odors can range from rotting flesh to a spring meadow, though most cases report unpleasant aromas...

 respectively. Anosmia and hyposmia

Hyposmia

Hyposmia is a reduced ability to smell and to detect odours. A related condition is anosmia, in which no odours can be detected. Some of the causes of olfaction problems are allergies, nasal polyps, viral infections and head trauma...

 (a less severe form of anosmia with a decreased sensitivity to smell but not the complete lack of it) are more quantitative disabilities typified by degrees in which the odor is sensed. Parosmia and phantosmia are more qualitative disabilities that are denoted by the impromptu introduction of odors without the proper stimulus.

Anosmia

Anosmia is characterized by the inability to detect odors. This particular dysfunction can be acute

Acute

Acute may refer to:* Acute accent* Acute angle* Acute * Acute * Acute toxicity...

 or chronic

Chronic

Chronic may refer to:* Chronic , a disease that is long-lasting and reoccurring.* Chronic toxicity, a substance with toxic effects after continuous or repeated exposure* The Chronic, a 1992 album by Dr. Dre...

, and can also by odor specific. The several different types of anosmia suggest several different causes for the symptoms. While anosmia can occur due to a physical obstruction or infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

, it can also be attributed to neurological damage. Acute anosmia tends to be associated with a blockage or infection; specific types of neurological damage are more closely associated with chronic anosmia. There are also cases of people born without the ability to detect odors; they are called anosmics.

Parosmia

Parosmia, or troposmia, is defined by patients incorrectly identifying odors, often mistaking pleasant or neutral odors for unpleasant ones. In order to effectively diagnose parosmia, as well as related diseases such as anosmia, diagnostic tool kits or “Sniffin’ Sticks” can be used to gauge a graded stimulus and measure the response of the patient. One example of parosmia involved using a peppermint

Peppermint

Peppermint is a hybrid mint, a cross between the watermint and spearmint . The plant, indigenous to Europe, is now widespread in cultivation throughout all regions of the world...

 “Sniffin’ Stick” by placing it in front of a patient’s nose, then the patient reporting a foul or rotten smell. As with anosmia, some cases of parosmia seemed to be odor specific, whereas other parosmias were more general and several smells were misinterpreted.

Phantosmia

Phantosmia is very similar to parosmia. Both usually result in unpleasant odors in the absence of the corresponding stimulus. Their difference is that parosmia is triggered by other odors; phantosmia is seemingly random. Phantosmia’s etymology

Etymology

Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...

is relatively straightforward, a phantom odor; it can be thought of as essentially an olfactory hallucination.