Question explored with the scientific record
What infections can cause a loss of smell and taste
The short version: COVID-19 is the standout cause of smell and taste loss, but it is far from the only one.
The strongest evidence points to SARS-CoV-2. A 2025 meta-analysis of 50 studies with over 14 million people found that infected people were about 4 times more likely to report loss of smell and about 3.7 times more likely to report loss of taste than uninfected controls [1]. The mechanism is becoming clearer: the virus enters supporting cells in the nose, not the smell neurons themselves, through ACE2 and TMPRSS2 receptors, and damages the tissue enough to knock out smell [2, 3]. Most people recover within days, but a minority do not [4].
The retrieval is thin on the rest. Influenza, other cold viruses, and sinus infections can all cause temporary smell loss through simple nasal blockage, but the records here do not directly compare them to COVID-19. One CDC guideline notes that most sinusitis cases are viral and that bacterial complications are rare, which matters because a blocked nose from any respiratory infection can dull smell [7]. Herpes viruses appear in the records mainly for eye and brain complications, not smell loss [5, 6].
| Cause | Smell loss | Taste loss | Recovery |
|---|---|---|---|
| COVID-19 | About 4x higher risk than uninfected [1] | About 3.7x higher risk [1] | Most within days [4] |
| Common cold / flu | Common, via nasal blockage | Less common | Usually with the cold |
| Bacterial sinusitis | Possible, via blockage | Rare | With treatment [7] |
The practical point: sudden smell loss with no stuffy nose is a strong COVID-19 signal. Smell loss with a blocked nose could be any respiratory virus. If smell loss persists for weeks, that is worth investigating, not dismissing.
My call: COVID-19 is the infection most strongly tied to smell and taste loss in the evidence, but any respiratory infection that blocks or inflames the nose can do it. Confidence: moderate, because the retrieval compares COVID-19 to uninfected people but does not directly compare it to other respiratory infections.
Sources used 7
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The risk of Long Covid symptoms: a systematic review and meta-analysis of controlled studies
This systematic review and meta-analysis of 50 studies involving over 14 million participants reveals a significantly increased risk of 39 out of 40 long Covid symptoms in individuals infected with SARS-CoV-2 compared to uninfected controls, with the highest risks observed for l…
DOI: 10.1038/s41467-025-59012-w -
Comparative assessment of the role of TMPRSS2 and ACE-2 receptors in the development of olfactory disorders in infection with coronavirus SARS-CoV-2
Autopsy-derived olfactory epithelium from COVID-19 patients shows TMPRSS2 broadly expressed on olfactory cells and ACE-2 mainly on sustentacular cells, with reduced OMP and ACE-2 positivity in those with olfactory disorders, implicating receptor involvement in SARS-CoV-2–related…
DOI: 10.26641/1997-9665.2024.1.78-82 -
Re-Print Cell Impact: Pathophysiological Mechanism of Sars-Cov-2 in the Olfactory and Gustatory System
A bibliographic review describing proposed pathophysiological mechanisms by which SARS-CoV-2 affects smell (anosmia) and taste (ageusia), highlighting ACE2/TMPRSS2 involvement in the olfactory epithelium, possible desquamation and basal cell regeneration, and noting fluctuating …
DOI: 10.31579/2640-1045/082 -
<p>Loss of Taste and Smell are Common Clinical Characteristics of Patients with COVID-19 in Somalia: A Retrospective Double Centre Study</p>
Retrospective, double-center study in Mogadishu, Somalia, of 60 adults with RT-PCR–confirmed COVID-19 pneumonia showing a high prevalence of olfactory/gustatory dysfunction (anosmia and/or ageusia) and detailing onset, recovery, and associated symptoms.
DOI: 10.2147/IDR.S263632 -
High prevalence of herpes simplex virus type 2 in acute retinal necrosis syndrome associated with herpes simplex virus in Japan
This study identifies herpes simplex virus type 2 as the major causative agent in acute retinal necrosis syndrome in Japan, based on molecular and serological analyses of 16 patients.
DOI: 10.1016/S0002-9394(99)00391-8 -
Viral causes of the acute retinal necrosis syndrome
This study investigates the viral causes of acute retinal necrosis syndrome, primarily focusing on the roles of varicella zoster virus and herpes simplex viruses, and highlights the importance of polymerase chain reaction techniques in diagnosing and guiding treatment for this c…
DOI: 10.1097/00055735-200106000-00008 -
Principles of appropriate antibiotic use for acute rhinosinusitis in adults: Background
A CDC-published guideline outlining judicious antibiotic use for acute rhinosinusitis in adults, emphasizing that most cases are viral, outlining diagnostic criteria to identify bacterial infection (typically ≥7 days with unilateral facial pain and purulent discharge), recommend…
DOI: 10.1067/s0196-0644(01)70089-3