Hyposmia: Why do people lose their sense of smell?
Scientists say that the human olfactory system, which governs the sense of smell, can detect between 10,000 and 100 billion different odors.
The sense of smell can help create and recall memories, and it can add to the pleasure of many everyday experiences, improving a person's quality of life.
Olfactory information also plays a crucial role in keeping a person physically safe. A loss of sense of smell can increase the risk of not noticing warning signs, such as the smell of gas, fire, or spoiled food. It can also indicate a more serious condition that needs medical attention.
According to the National Institutes of Health, 12% of adults in the United States have some loss of their sense of smell. This issue becomes more common with age.
Hyposmia refers to the loss of the sense of smell.
Possible causes of hyposmia include:
- a head injury
- infections, such as the flu
- small growths called polyps in the nose or sinuses
- a deviated nasal septum
- chronic sinus problems
- a hormonal imbalance
- dental problems
Some medications can also affect the sense of smell.
- several antibiotics, including ampicillin and tetracycline
- some antidepressants, such as amitriptyline
- certain antihistamines, such as loratadine
Other factors that could contribute to a loss of the sense of smell include:
- long-term exposure to certain chemicals
- tobacco smoking
- the use of recreational drugs, such as cocaine
- radiation treatment for cancers of the head and neck
Hyposmia can be a sign of an underlying condition.
Hyposmia can also be a sign of other health issues, including the following neurological conditions:
The findings of a 2013 study of 50 people suggested that 40% of those with MS may have at least a partial loss of their sense of smell.
A reduced sense of smell does not necessarily mean that a person will develop one of these conditions, but some experts have suggested that a smell screening test could aid early diagnosis.
Other conditions that can affect the sense of smell include:
Researchers have also found that people with type 1 diabetes can have trouble detecting and distinguishing scents.
Other changes to the sense of smell
Hyposmia is the partial loss of the sense of smell, but some people may experience other issues with this sense.
For example, anosmia is the complete loss of the sense of smell.
Some people have anosmia from birth, but it can sometimes result from a head injury, a problem with the nasal passages, such as chronic inflammatory nasal or sinus disease, or a severe viral infection of the upper respiratory tract.
Other types of smell dysfunction are:
- Parosmia, which is when the perception of smells becomes distorted, so smells that used to be pleasing start to seem unpleasant, or an odor appears to change in intensity.
- Phantosmia, which is when a person believes that they can smell something, but it is not actually there.
Hyposmia that is due to a seasonal allergy or a cold usually improves without treatment, but some medications and types of therapy to retrain the sense of smell may help.
If a person loses their sense of smell after a head injury or a significant inflammatory injury to the olfactory system, a complete recovery may not be possible.
According to the Anosmia Foundation, up to 22% of cases have no clear cause.
Diagnosis and treatment
A physical examination may reveal the reason for hyposmia.
If a person starts to lose their ability to smell for no apparent reason, they should seek medical help, especially if the change is sudden and severe.
A doctor will carry out a physical examination. They will check the nasal passages, sinuses, and surrounding structures.
They will also ask about the person's medical history, especially that of upper respiratory problems, and if they are experiencing any other symptoms.
A nose and throat specialist (otolaryngologist) may perform a nasal endoscopy, in which they insert a long, thin tube with a camera on it into the person's nose to inspect the nasal and sinus cavities.
A doctor will be looking for signs of:
- growths that could indicate polyps or a tumor
- enlarged nasal structures
- a deviated nasal septum
If these tests do not reveal a cause, the doctor may recommend an MRI scan to assess the areas in the brain that detect smells.
A scratch-and-sniff test or tests with "Sniffin' Sticks" can help a doctor determine whether someone has anosmia or hyposmia. In cases of hyposmia, these tests will measure the extent of the loss of smell.
Treatment options include medication, surgery, and any necessary therapy for an underlying condition.
The doctor may recommend surgery for:
- nasal polyps
- a deviated septum
- other structural problems
They may prescribe medications, such as steroids and antihistamines, to calm any inflammation resulting from an allergy or respiratory infection.
Many people start to lose their sense of smell as they become older. This loss can increase the risk of eating spoiled food and not noticing the signs of danger, such as a fire. It can also indicate a health problem that may need attention.
People who start to lose their sense of smell should seek treatment to ensure that these changes do not cause additional health and safety problems and to get treatment for any underlying conditions.
Installing and maintaining carbon monoxide and smoke alarms in the home can help protect people who have started to lose their sense of smell.
People should also use caution when working with potentially toxic household chemicals and check any food expiration dates.