Losing smell became one of COVID’s best-known signs because it often arrives suddenly, sometimes with no stuffy nose at all. The virus mostly isn’t damaging the nerves that detect smells. It knocks out the cells that keep those nerves working.1PubMed Central. Olfactory dysfunction in COVID-19: new insights into the underlying mechanisms For most people that makes it a temporary outage rather than permanent nerve damage, which is why smell usually returns once the nose repairs itself. Much of what feels like lost taste is actually lost smell, since flavour depends heavily on the nose.2PubMed Central. The taste of the pandemic—contemporary review on the current state of research on gustation in coronavirus disease 2019 (COVID‐19)
The Virus Targets the Cells That Support Smell Nerves
Smell is detected by a stamp-sized patch of lining high inside the nose. Smell nerves send fine, hair-like tips into a layer of mucus there, and odour molecules dissolve into that mucus and touch the tips. Around each nerve sit support cells, which feed and protect the nerves and help shape the mucus. The virus gets into cells through a doorway protein called ACE2, helped by another protein called TMPRSS2.
In human nose tissue, ACE2 and TMPRSS2 are found on support cells and on the stem cells that rebuild the lining, but not on mature smell nerves.3PubMed Central. Non-neuronal expression of SARS-CoV-2 entry genes in the olfactory system suggests mechanisms underlying COVID-19-associated anosmia So the support cells and stem cells, not the nerves, are the virus’s likely direct targets.4PubMed Central. Non-neuronal expression of SARS-CoV-2 entry genes in the olfactory system suggests mechanisms underlying COVID-19-associated anosmia Human tissue examined after death and infected animals both show infected support cells while the smell nerves stay free of virus.5PubMed Central. SARS-CoV-2 infection of sustentacular cells disrupts olfactory signaling pathways Support cells also carry a protein that can make infected cells fuse into large clumps, one possible way they’re destroyed.6PubMed. Supporting Cells of the Human Olfactory Epithelium Co-Express the Lipid Scramblase TMEM16F and ACE2 and May Cause Smell Loss by SARS-CoV-2 Spike-Induced Syncytia
This is why COVID differs from a cold. A cold usually dulls smell through swelling and congestion that stop odours reaching the patch. COVID often takes smell with a clear nose, because the damage is inside the smell lining itself. Blowing your nose or taking decongestants doesn’t fix it.
How Losing Support Cells Switches Smell Off
When infected support cells die, the mucus around the smell nerves changes composition.7PubMed Central. Olfactory dysfunction in COVID-19: new insights into the underlying mechanisms The nerves’ hair-like tips, where odours are actually caught, pull back.8PubMed Central. Olfactory dysfunction in COVID-19: new insights into the underlying mechanisms Support cells likely supply sugar into the mucus that powers smell signalling in those tips, so without them the tips lose their fuel.9PubMed Central. Olfactory dysfunction in COVID-19: new insights into the underlying mechanisms In infected hamsters, large numbers of support cells were damaged and the sensing tips largely lost.10PubMed Central. “Anosmia” the mysterious collateral damage of COVID-19
The nerves also go quiet from the inside. In infected hamsters, smell nerves stayed alive and uninfected but sharply switched down the genes for smell receptors.11PubMed Central. Revealing the mystery of persistent smell loss in Long COVID patients The packing of their DNA was reorganised, pulling apart gene clusters that normally work together.12PubMed Central. Revealing the mystery of persistent smell loss in Long COVID patients A nerve can therefore be present yet temporarily unable to detect odours, a second reason smell can go blank.
Inflammation adds to the damage early on. Noses of people with active COVID showed raised levels of an inflammation signal in the smell lining, so inflammation of the lining itself likely contributes to sudden smell loss.13PubMed. Proinflammatory Cytokines in the Olfactory Mucosa Result in COVID-19 Induced Anosmia
Over the weeks after infection, stem cells rebuild the support layer, then the nerve tips regrow and smell returns, often gradually and patchily. That patchiness is why smell can come back in waves rather than all at once. The lining repairs unevenly, patch by patch, so some smells may return before others.
Why Food Tastes Flat When It’s Really Your Nose
The tongue detects only sweet, salty, sour, bitter and savoury. The rest of flavour comes from aromas rising from the mouth to the back of the nose. People often blame taste when the real loss is this “smelling from behind.”14PubMed Central. Varied Effects of COVID-19 Chemosensory Loss and Distortion on Appetite: Implications for Understanding Motives for Eating and Drinking About half of people with COVID report taste loss, but careful testing finds true taste loss in up to about a quarter.15PubMed Central. The taste of the pandemic—contemporary review on the current state of research on gustation in coronavirus disease 2019 (COVID‐19) Some people can tell sweet from salty yet can’t identify foods, which points to lost smell.16PubMed Central. Persistent Olfactory and Taste Dysfunction after COVID-19
Real taste damage can happen too. Taste bud cells carry ACE2, and replicating virus has been found in taste cells of people with taste problems.17PubMed Central. Treatments of COVID-19-Associated Taste and Saliva Secretory Disorders
A kitchen check can help you tell which is which. Pinch your nose and taste sugar, salt and lemon. If you can name sweet, salty and sour, your taste buds work. If food still tastes of nothing with your nose open, smell is the missing part. Tell your doctor which kind it seems to be.
Meanwhile, you can make food more enjoyable. Lean on tastes the tongue still detects, like salt, acid and sweetness. Add texture, temperature contrast and spice heat, none of which depend on smell. Just watch that piling on salt or sugar doesn’t become a habit.
Why Smell Loss Lasts for Some People
In people with long-lasting smell loss, nose samples show immune T cells spread through the smell lining, yet no virus was detectable in that tissue.18PubMed Central. Persistent post–COVID-19 smell loss is associated with immune cell infiltration and altered gene expression in olfactory epithelium Support cells behaved as if still responding to inflammation, and there were fewer smell nerves than normal.19PubMed Central. Persistent post–COVID-19 smell loss is associated with immune cell infiltration and altered gene expression in olfactory epithelium Lingering immune inflammation, not lingering virus, may therefore keep smell from returning.20PubMed Central. Persistent post–COVID-19 smell loss is associated with immune cell infiltration and altered gene expression in olfactory epithelium
The brain’s smell areas may change too. In brain scans of people with persistent smell loss, about 4 in 10 have a smell bulb, the first brain relay for smell, that is smaller than normal.21PubMed Central. Olfactory Bulb MRI and Paranasal Sinus CT Findings in Persistent COVID-19 Anosmia People with lasting smell loss had less grey matter in smell-related brain areas than recovered patients,22PubMed Central. Structural brain changes in post‐acute COVID‐19 patients with persistent olfactory dysfunction and even after mild COVID, scans have shown shrinking in brain regions linked to smell.23PubMed Central. Reduced olfactory bulb volume accompanies olfactory dysfunction after mild SARS-CoV-2 infection These scans can’t yet show whether the changes cause the loss or follow from not using smell.
Persistent loss is a minority outcome: most people regain smell within weeks to a few months. Many who are still affected keep improving slowly, sometimes over a year or more, so a long gap doesn’t mean recovery has stopped. Nerves are replaced throughout life, so a lining with fewer smell nerves can in principle be rebuilt once inflammation settles.
See a doctor if smell hasn’t returned after a few months. Seek care sooner if the loss is on one side, or comes with nosebleeds or blockage. An ear, nose and throat specialist can test smell and discuss treatment.
Why Some People Lose Smell and Others Don’t
Smell loss became much less common once Omicron arrived.24PubMed Central. Why Does the Omicron Variant Largely Spare Olfactory Function? Implications for the Pathogenesis of Anosmia in Coronavirus Disease 2019 Omicron prefers a different entry route than the TMPRSS2 doorway that support cells carry in abundance.25PubMed Central. Why Does the Omicron Variant Largely Spare Olfactory Function? Implications for the Pathogenesis of Anosmia in Coronavirus Disease 2019 Support cells have strong defences against that other route.26PubMed Central. Prevalence of Olfactory Dysfunction with the Omicron Variant of SARS-CoV-2: A Systematic Review and Meta-analysis Omicron’s changes may also make it dissolve less well in nasal mucus, so less reaches the smell patch.27PubMed Central. Prevalence of Olfactory Dysfunction with the Omicron Variant of SARS-CoV-2: A Systematic Review and Meta-analysis
Children are affected less. About 16% of children with COVID had smell loss, compared with about 43% of adults.28PubMed Central. Prevalence of Smell or Taste Dysfunction Among Children With COVID-19 Infection: A Systematic Review and Meta-Analysis Taste loss was about 9% in children versus about 45% in adults.29PubMed Central. Prevalence of Smell or Taste Dysfunction Among Children With COVID-19 Infection: A Systematic Review and Meta-Analysis Children’s noses and mouths may carry less ACE2.30PubMed Central. Prevalence of Smell or Taste Dysfunction Among Children With COVID-19 Infection: A Systematic Review and Meta-Analysis Teenagers are more often affected than younger children,31PubMed Central. Loss of smell and taste in COVID-19 infection in adolescents and older children are the most likely to notice and say so.32Children’s Hospital of Philadelphia. Loss of Smell in the COVID-19 Era: When to Worry
Genes play a part as well. People with certain versions of a particular gene region were more likely to lose smell or taste with COVID.33PubMed. The UGT2A1/UGT2A2 locus is associated with COVID-19-related loss of smell or taste These genes work in the smell lining, helping process odours.34PubMed. The UGT2A1/UGT2A2 locus is associated with COVID-19-related loss of smell or taste
If you’ve had COVID more than once, losing smell the first time doesn’t mean you’ll lose it every time. A later Omicron-era infection is less likely to take smell, so smell loss alone is no longer a reliable sign of COVID.
Your Sense of Smell May Be Weaker Than You Think
About 8 in 10 people who said their smell changed after COVID scored abnormal on a scratch-and-sniff test.35PubMed Central. Olfactory Dysfunction After SARS-CoV-2 Infection in the RECOVER Adult Cohort About 2 in 10 had severe loss or anosmia, meaning complete smell loss.36PubMed Central. Olfactory Dysfunction After SARS-CoV-2 Infection in the RECOVER Adult Cohort Yet two-thirds of infected people who noticed no change still tested below normal.37PubMed Central. Olfactory Dysfunction After SARS-CoV-2 Infection in the RECOVER Adult Cohort Among people never infected, 6 in 10 also tested low, so low scores aren’t all from COVID.38PubMed Central. Olfactory Dysfunction After SARS-CoV-2 Infection in the RECOVER Adult Cohort Of people who felt fully recovered at six months, only about 4 in 10 tested normal.39PubMed Central. Six-Month Psychophysical Evaluation of Olfactory Dysfunction in Patients with COVID-19 And only about a third of people with tested smell loss were aware of it before testing.40PubMed Central. Olfactory dysfunction in COVID-19; Self-report or olfactory dysfunction test?
Smell fades or returns gradually, and the brain adapts to a new normal, so a partial loss can go unnoticed day to day. Flavour can also feel almost normal because taste, texture and heat still work, which masks a weaker nose.
To get your smell checked, doctors may use a scratch-and-sniff booklet of about 40 odours. You pick each odour from multiple choices, and the score shows mild, moderate, severe or complete loss. Home tests with labelled jars give a rough check.
Helping Your Sense of Smell Recover
Smell training means sniffing a set of strong scents, often rose, lemon, clove and eucalyptus, twice daily for months. Repeated odour stimulation can help the smell lining regrow nerves and restore receptor activity.41PubMed Central. Olfactory training with essential oils for patients with post-COVID-19 smell dysfunction: A case series Training can also strengthen brain smell areas and increase smell bulb size.42PubMed Central. Olfactory training with essential oils for patients with post-COVID-19 smell dysfunction: A case series
To do it properly, sniff each scent for about 20 seconds while picturing it. Do it morning and evening, every day. Keep going at least three months even without early change, and swap scents after a few months to keep stimulating the nose.
Medical options are emerging. Injecting a concentrate of the patient’s own blood platelets into the smell area improved smell more than a dummy treatment at 3 months.43PubMed. Use of platelet-rich plasma for COVID-19-related olfactory loss: a randomized controlled trial About 57% responded versus about 8% on placebo.44PubMed. Use of platelet-rich plasma for COVID-19-related olfactory loss: a randomized controlled trial It improved telling smells apart, not naming them or detecting faint ones.45PubMed. Use of platelet-rich plasma for COVID-19-related olfactory loss: a randomized controlled trial Ask a specialist whether such treatments are offered.
Some people find familiar things smell wrong, often foul, which is called parosmia, or distorted smell. It often appears as regrowing nerves reconnect and can be a sign of recovery rather than worsening. Common triggers are coffee, onion, meat and toothpaste. Bland, cool foods often trigger less. Keep training, as distortions usually fade over months.
Staying Safe and Well Without Smell
Smell normally warns us of fire, gas leaks and spoiled food.46PubMed Central. Effects of COVID-19 on Sense of Smell: Human Factors/Ergonomics Considerations Over half of people with COVID smell loss reported at least one safety problem.47PubMed Central. Quality of life and safety impact of COVID-19 associated smell and taste disturbances The most common was not smelling smoke others could, in about 45%.48PubMed Central. Quality of life and safety impact of COVID-19 associated smell and taste disturbances Check the cooker is off visually, keep a working smoke alarm and check food expiry dates.49NHS inform. Long COVID: Loss of smell or taste A gas detector adds protection where gas is used.
Date leftovers and throw them out on schedule. Ask someone else to check for gas or burning, and use a timer when cooking. If you worry about body odour, ask a trusted person.
Over half of people with COVID smell loss also reported psychological distress.50PubMed Central. Olfactory-related quality of life impacts psychological distress in people with COVID-19: The affective implications of olfactory dysfunctions Losing smell’s role in intimate life and in using perfume was linked with the most distress.51PubMed Central. Olfactory-related quality of life impacts psychological distress in people with COVID-19: The affective implications of olfactory dysfunctions Talk to a doctor if smell loss is affecting your mood.