Loss of Smell (Anosmia): How It Impacts Safety, Health, and Mortality

More and more people struggle with and complain about changes in their sense of smell. In this article we will focus on three forms of this, anosmia, hyposmia and parosmia, how often they occur, the impact and the most common causes. In subsequent articles we will address how to treat and relieve these conditions.

Key Definitions

Related conditions are dysgeusia, which is a distorted sense of taste and ageusia, which is complete loss of taste. Our tongue can only discern five flavors (salty, sour, sweet, bitter, umami (savory) and most of what people think is taste is actually scent. Here, we will focus on anomia, hyposmia and parosmia. 

The major Impacts of Anosmia and Parosmia

The impact of anosmia is significant. People who have a very impaired (hyposmia) or absent (anosmia) sense of smell are unable to smell if there’s a gas leak, or a fire or similar threat, which can be dangerous. They are also unable to determine if foods have gone off and may eat rotten food, another danger. They may even ingest harmful substances that a properly working sense of smell would deter us from. They may be unable to smell their own body odor, which can be socially challenging, but also prevent them from telling if they have a disease that changes their odor, e.g. an abscess, skin ulcer, etc. 

With parosmias, the usual enjoyment of food and pleasant aromas can be impaired and lead to decreased food intake and even starvation, which I have seen in former clients with severe OCD (obsessive compulsive disorder) or psychosis. Parosmias can also interfere with the above-mentioned abilities, e.g. to detect gas leaks or fires, since the characteristic odors may not be correctly identified, and impair the ability to determine if food is spoiled or a substance is noxious. 

There is a correlation between anosmia and depression. People with impaired olfaction have more symptoms of depression that worsen with severity of smell loss and people who are depressed have a decreased sense of smell. (Kohli et. al. 2016)

Even more alarming, olfactory dysfunction was one of the strongest predictors of 5 year mortality in older adults, more than heart failure, lung disease and cancer. (Pinto, et. al. 2014)

In summary, having a properly functioning sense of smell doesn’t just allow us to enjoy a wide range of olfactory stimuli, but can also alert us to danger, spoiled foods and other aspects that are important for quality of life. An impaired or absent sense of smell can not only cause problems but be dangerous, cause depression and be a harbinger of mortality.

How Often Does Smell loss (Anosmia) And What are the Causes?

There are many possible causes for anosmia, hyposmia and parosmia.

These include both bacterial and viral infections, for example COVID-19. It’s important to note that both anosmia and parosmia caused by viral infections occurred before COVID-19, such as the common cold and influenza. (Rebholz, et. al. 2020) Anosmia and parosmia are not infectious, but if they are due to infections, these infections can be contagious. Another common cause is acute sinusitis, meaning a sudden inflammation of the sinus cavities around the nose. 

Significant head injury can cause physical damage to the olfactory bulb and thus anosmia or parosmia.

There are a variety of other conditions that can cause anosmia or parosmia, including but not limited to certain medications, cancer treatments, smoking, chemical exposure, chronic dry mouth and others. Surgery of or around the nose can also cause anosmia. (Briner, et. al. 2003)

Acquired vs congenital loss of smell

There are two main kinds of anosmia, congenital, which means since birth, and acquired, which means it started at some point later in life, and the person was able to smell before (Li 2025). Overall 20% of the adult population experience anosmia. (Rebholz et. al. 2020)

Infection induced anosmia

Most cases, i.e. 50-70%, of anosmia happen due to inflammation and obstruction. This can be due to sinus disease, nala polyps, inflammation of the nasal mucosa and other obstruction. (Deems et. al. 1991) A variety of viral or bacterial infections can cause anosmia, including the COVID-19 virus. For COVID, loss or impairment in scent can be the first presenting symptom, more commonly in younger patients. (Wu et. al. 2023) A meta-analysis of several studies showed that the prevalence is 47%, with a wide range (11-84%) (Borsetto 2020). Anosmia remains persistent in up to 7% of patients one year after diagnosis. (Wu et. al. 2023) While loss or decrease in sense of smell has been used as a self-assessment for COVID infection (Sudre, et. al. 2021), it can also be due to other infections.

Most cases of anosmia do get better. (Rebholz et. al. 2020)

Trauma induced Anosmia

Another cause of anosmia is head trauma and the severity of the head trauma correlates with the rate of anosmia, ranging from 0-16% for a mild traumatic brain injury (TBI), to 25-30% for a severe TBI.  The usual mechanism in cases of head trauma are shear injuries from head trauma, that sever the olfactory nerves in the cribriform plate, which is the thin bony plate that separates the top of the from the olfactory bulb above it. These cases of anosmia are often not noticed until later. (Proskynitopoulos, et. al. 2016) Even in cases when anosmia is due to TBI, a certain percentage (41%) of patients recover. Patients whose traumatic brain injury does not include a fracture have a higher rate of recovery. (Joung et. al. 2007) 

Age, degeneration and smell loss

Other causes of anosmia include both age related changes, but also it has been associated with neurodegenerative diseases, such as Parkinson’s Disease, Alzheimer’s and other dementias (e.g. Lewy Body dementia) and often precedes the main symptoms of diseases by years and thus screening for changes in olfactory perception could serve as an early warning for the subsequent development of these serious conditions. (Fatuzzo, et. al. 2023)

Parosmia follow the same patterns than Anosmia

Parosmia is common has become more common since COVID-19. When measuring olfactory dysfunction using objective assessment, the rate in the general population was 28.8% and much higher than subjective assessment (9.5%) (Desiato et. al. 2021) This indicates that having a reliable, objective assessment is important and can detect olfactory problems that people themselves may not even be aware of.

Summary of causes

In summary, the most common causes of anosmia are infections and sinus inflammation. Traumatic Brain Injuries can also cause anosmia, with the severity proportional to the severity of the head injury. Changes in olfactory perception can also be a sign of neurodenerative disorders such as Parkinson’s and Alzheimer’s often years before these conditions become severe and diagnosable. Nevertheless, the majority of cases of anosmia do improve, sometimes over months.

What can you do about anosmia?

One of the most effective, research-backed methods is Olfactory Training—using essential oils to gently retrain your sense of smell over time.

We cover everything you need to know in our next article:
👉 [Start Smell Training: Using Essential Oils for Anosmia Recovery]