Hyperosmia is an increased

olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...

acuity (heightened sense of smell), usually caused by a lower

threshold for odor The odor detection threshold is the lowest concentration of a certain odor compound that is perceivable by the human sense of smell. The threshold of a chemical compound is determined in part by its shape, polarity, partial charges, and molec ...

. This perceptual disorder arises when there is an abnormally increased signal at any point between the

olfactory receptor Olfactory receptors (ORs), also known as odorant receptors, are chemoreceptors expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants (for example, compounds that have an odor) which give ri ...

s and the olfactory cortex. The causes of hyperosmia may be genetic, hormonal, environmental or the result of

benzodiazepine withdrawal syndrome Benzodiazepine withdrawal syndrome often abbreviated to benzo withdrawal or BZD withdrawal is the cluster of signs and symptoms that may emerge when a person who has been taking benzodiazepines, either medically or recreationally develops a p ...

Causes

Genetics

A study by Menashe et al. has found that individuals with a single nucleotide polymorphism variant in the OR11H7P pseudogene have a lower receptor activation threshold for isovaleric acid. These individuals are hyperosmic for this single odorant. Another study by Keller et al. has found that people with the intact human odorant receptor OR7D4 are more sensitive to

androstenone Androstenone (5α-androst-16-en-3-one) is a 16-androstene class steroidal pheromone. It is found in boar's saliva, celery cytoplasm, and truffle fungus. Androstenone was the first mammalian pheromone to be identified. It is found in high concent ...

and

androstadienone Androstadienone, or androsta-4,16-dien-3-one, is a 16-androstene class endogenous steroid that has been described as having potent pheromone-like activities in humans. The compound is synthesized from androstadienol by 3β-hydroxysteroid dehydro ...

and thus find them unpleasant (individuals with the semi-functional OR7D4 have two non-synonymous single nucleotide polymorphisms in the OR7D4 pseudogene, resulting in two amino acid substitutions). There has not yet been extensive research into the genetic background of those with general hyperosmia, rather than for just a single odorant.

Environmental

There has not been extensive research into environmental causes of hyperosmia, but there are some theories of some possible causes. In a study by Atianjoh et al., it has been found that

amphetamines Substituted amphetamines are a class of compounds based upon the amphetamine structure; it includes all derivative compounds which are formed by replacing, or substituting, one or more hydrogen atoms in the amphetamine core structure with sub ...

decrease levels of dopamine in the olfactory bulbs of rodents. On this basis, it has been hypothesized that amphetamine use may cause hyperosmia in rodents and humans, but further research is still needed. Anecdotal support for the belief that amphetamines may cause hyperosmia comes from

Oliver Sacks Oliver Wolf Sacks, (9 July 1933 – 30 August 2015) was a British neurologist, naturalist, historian of science, and writer. Born in Britain, Sacks received his medical degree in 1958 from The Queen's College, Oxford, before moving to the Uni ...

's account of a patient (who he later revealed to be himself) with a heightened sense of smell after taking amphetamines. It has been observed that the inhalation of hydrocarbons can cause hyperosmia, most likely due to the destruction of dopaminergic neurons in the olfactory bulb. Methotrexate, administered in the treatment of psoriasis, has been known to cause hyperosmia, and may be more likely to do so in patients with a history of migraines.Abstract
However, this is only an observation and not part of a study; therefore, it is yet to be verified.

Treatment

Normal olfactory acuity will usually return over time if the cause is environmental, even if it is untreated. The hyperosmic person may need to be removed from strong odorants for a period of time if the sensation becomes unbearable. Before they had been discontinued due to undesirable side effects,

butyrophenones Butyrophenone is an organic compound with the formula C6H5C(O)C3H7. It is a colorless liquid. The butyrophenone structure—a ketone flanked by a phenyl ring and a butyl chain—forms the basis for many other chemicals containing various sub ...

thioridazine hydrochloride Thioridazine (Mellaril or Melleril) is a first generation antipsychotic drug belonging to the phenothiazine drug group and was previously widely used in the treatment of schizophrenia and psychosis. The branded product was withdrawn worldwi ...

, both of which are dopamine antagonists, have been used to treat hyperosmia.

References

External links