Post-COVID Smell Loss: Why It Happens, When It Recovers, and the Role of PRP

By Dr Vyas M.N. Prasad, FRCS (ORL-HNS) Consultant Otolaryngologist & Head and Neck Surgeon, Camden Medical Centre, Singapore

Loss of smell after COVID-19 occurs because the virus damages the supporting cells of the olfactory epithelium rather than simply blocking the nose — which is why it can persist long after the infection resolves. Smell training started early gives the best chance of recovery, and for persistent cases beyond six months, Platelet-Rich Plasma (PRP) therapy injected directly into the olfactory niche is available at Absolute ENT, Singapore.

• COVID-19 damages the supporting cells of the olfactory epithelium — not simply the nose — which is why smell loss can persist long after infection

• Smell training started early gives the best chance of natural recovery

• For persistent cases beyond six months, Platelet-Rich Plasma (PRP) therapy to the olfactory area is a newer treatment option

• This post covers the mechanism, recovery timeline, and role of PRP

For a broader overview of all causes of smell loss and treatment, read this post.

Post-COVID smell loss affects a significant minority of patients long after the infection resolves. Unlike a blocked nose from a cold, the damage occurs in the olfactory epithelium itself — which is why it persists and why specific treatment is needed

Loss of smell after COVID-19 is one of the most distinctive and, for many patients, distressing legacies of the pandemic. Most people expect it to resolve quickly — and for many it does. But for a significant minority, smell loss persists for months or even years, affecting the enjoyment of food, the detection of hazards, and a quality of life that is often underestimated until the sense is gone.

At Absolute ENT, I assess and treat post-COVID smell loss with a structured approach that includes olfactory retraining and, in selected cases, Platelet-Rich Plasma (PRP) therapy — an emerging intervention with promising early evidence for patients who have not responded to standard treatment.

How COVID-19 Affects the Sense of Smell

The mechanism by which COVID-19 causes smell loss is different from most other viral illnesses. In a typical cold or flu, loss of smell is usually conductive — swelling and congestion block odour molecules from reaching the smell receptors high in the nasal cavity. This resolves as the congestion clears.

COVID-19, by contrast, appears to cause sensorineural smell loss — damage to the olfactory system itself rather than simply a mechanical blockage. The SARS-CoV-2 virus infects supporting cells (sustentacular cells) in the olfactory epithelium — the specialised tissue lining the top of the nasal cavity where smell is processed. These supporting cells are essential for the function and survival of the olfactory receptor neurons. When they are damaged, the neurons lose their support and begin to dysfunction or die.

This explains why COVID-19 smell loss can occur even when the nose feels completely clear, and why it can persist long after the viral infection has resolved.

What Is Parosmia — and Is It a Good Sign?

Many patients who develop persistent smell loss after COVID-19 subsequently notice that smells return in a distorted form — coffee smells like petrol, food smells like rotting matter, or familiar scents are replaced by a single unpleasant chemical odour. This distortion is called parosmia.

Parosmia can be profoundly unpleasant and severely affects the enjoyment of food. However — and this is important — parosmia is generally considered a sign that the olfactory nerve is attempting to regenerate. The distorted signals reflect the early, imperfect reconnection of recovering nerve fibres. For most patients, parosmia eventually gives way to more normal smell perception, though the timeline is unpredictable and can be lengthy.

How Long Does Post-COVID Smell Loss Last?

Recovery varies considerably between individuals. Based on available evidence:

• The majority of patients recover meaningful smell function within the first three to six months

• Around 10 to 15% of those affected have persistent significant smell loss beyond six months

• A smaller proportion have incomplete or no recovery beyond one year

Factors associated with poorer recovery include older age, greater initial severity of smell loss, and longer duration before treatment is started. Early intervention — particularly early commencement of smell training — appears to improve outcomes.

Olfactory nerve fibres under electron microscopy, highlighting the delicate neural structures involved in smell perception

Assessment at Absolute ENT

When I see a patient with post-COVID smell loss, the assessment includes:

Clinical history — duration of smell loss, whether it was present from the acute infection or developed later, any parosmia or phantosmia (smelling something that is not there), and the trajectory of recovery so far.

Nasal endoscopy — to examine the nasal cavity and rule out any additional contributing pathology — nasal polyps, mucosal swelling, or anatomical obstruction that could be compounding the smell loss.

Smell identification testing — using validated tools to objectively measure smell function and provide a baseline against which response to treatment can be assessed.

MRI imaging — in selected cases, particularly when there is diagnostic uncertainty or the clinical picture is atypical.

Treatment: Olfactory Retraining

Smell training — also called olfactory retraining — is the best-evidenced intervention for post-viral smell loss and is the foundation of treatment.

The principle is based on the olfactory system's capacity for neuroplasticity — its ability to repair and rewire. By repeatedly and deliberately stimulating the olfactory receptors with strong, familiar scents, smell training is believed to support the regeneration and reconnection of olfactory nerve fibres.

How it works:

• Four distinct scents are chosen — traditionally rose, lemon, eucalyptus, and cloves, though personal familiarity with the scents may improve effectiveness

• The patient sniffs each scent for twenty seconds twice daily, concentrating on the memory of what that smell should be like

• Training is continued for a minimum of three to six months — consistency is more important than frequency

The evidence for smell training is robust relative to other interventions and it carries no risk of harm. It is suitable for all patients with post-COVID smell loss, regardless of how long they have had it. Earlier commencement is better, but late starters still benefit.

Platelet-Rich Plasma (PRP) for Post-COVID Smell Loss

For patients with persistent smell loss who have not achieved adequate recovery through smell training alone — typically those with symptoms lasting beyond six months — I offer Platelet-Rich Plasma therapy as an advanced treatment option.

What Is PRP?

PRP is prepared from the patient's own blood. A small blood sample is taken and placed in a centrifuge, which separates and concentrates the platelets. Platelets contain growth factors — naturally occurring proteins that support tissue repair, cell regeneration, and nerve recovery. By concentrating and delivering these growth factors directly to the site of injury, PRP aims to support the regeneration of olfactory tissue.

How Is It Administered?

Under gentle endoscopic guidance, the concentrated PRP is injected into the olfactory niche — the specialised area high in the nasal cavity where the smell receptors are located. This targeted delivery ensures that the growth factors are applied precisely to the affected tissue rather than being diluted systemically.

The procedure is performed in clinic. Local anaesthetic spray is applied to the nasal passages beforehand, and the treatment is well tolerated by most patients.

What Does the Evidence Show?

Research into PRP for post-COVID anosmia is still relatively recent, but early studies have shown promising results in terms of improved smell scores following treatment. The mechanism is biologically plausible — olfactory receptor neurons do have the capacity to regenerate, and growth factor delivery to the olfactory epithelium has a logical rationale.

It is important to be clear with patients that results are not guaranteed and vary between individuals. Some patients experience meaningful improvement; in others, the response is partial. PRP is offered as part of a structured treatment approach — alongside continued smell training — rather than as a standalone cure.

Who Is PRP Suitable For?

I consider PRP for patients who:

• Have post-COVID smell loss persisting beyond six months

• Have completed a course of structured smell training without adequate recovery

• Have no additional nasal pathology that would explain persistent symptoms, or have had such pathology treated

• Are medically suitable for a minor clinic procedure

A consultation is essential to assess suitability and discuss realistic expectations.

Practical Advice for Patients With Post-COVID Smell Loss

Start smell training now — do not wait to see whether smell returns on its own. Early training is associated with better outcomes, and there is no downside to starting.

Be patient — recovery from olfactory nerve damage is slow. Month-on-month progress may be imperceptible on a day-to-day basis. Using a smell diary to record periodic assessments can help track gradual improvement.

Manage parosmia practically — if parosmia is making certain foods intolerable, adapt your diet temporarily to avoid the worst triggers. Cold foods tend to have less volatile aroma and are often better tolerated than hot ones. Parosmia typically improves as recovery progresses.

Seek assessment if symptoms persist — there is no benefit in waiting indefinitely for spontaneous recovery if six months have passed without meaningful improvement. Assessment can confirm the diagnosis, exclude other causes, and open the door to treatment options including PRP.

Supplements — omega-3 fatty acids and Vitamin A drops have been proposed as supportive measures for olfactory recovery. Evidence remains preliminary, but the risk profile is low and they may be discussed at consultation.

Book an Assessment for Post-COVID Smell Loss

If you have lost your sense of smell following COVID-19 and have not recovered, or if smell has returned in a distorted form, a specialist ENT assessment can help establish where you are in the recovery process and what treatment options are appropriate.

Dr Vyas Prasad offers assessment and PRP treatment for post-COVID anosmia at Absolute ENT, Camden Medical Centre, 1 Orchard Boulevard, #09-08, Singapore. Contact the clinic by WhatsApp on +65 8060 8079 or by email at camden.mmc@gmail.com.