Post-COVID Smell Loss: Why Many Don’t Realize They’re Affected

The COVID-19 pandemic brought with it a host of strange and often debilitating symptoms, and one of the most widely reported was the abrupt loss of smell and taste. For many, this symptom was a clear indicator of infection, prompting immediate testing and isolation. However, as the world moved past the initial shock of the pandemic, a more subtle and insidious problem has emerged: millions of people may be living with “hidden” or “undetected” smell loss long after their COVID-19 infection, without even realizing it. This isn’t just a minor inconvenience; it’s a profound sensory deficit with significant implications for health, safety, and overall well-being.

During the early stages of the pandemic, particularly with the Alpha and Delta variants, an acute loss of smell (anosmia) or a reduced sense of smell (hyposmia) was a hallmark symptom. For many, this was a stark and undeniable experience. Food became bland, perfumes lost their essence, and the world suddenly seemed muted. People could clearly identify that their sense of smell was gone or severely diminished. This clear-cut symptom helped people recognize they had COVID-19 and prompted them to seek care or isolate.

However, as newer variants like Omicron emerged, the prevalence of reported smell loss seemed to decrease. This led some to believe the virus was evolving to be less neurotropic (less likely to affect the nervous system, including smell). While the acute, complete loss of smell might have become less common, scientists now understand that a more subtle form of olfactory dysfunction continued, often escaping conscious detection.

The concept of “hidden” or “undetected” smell loss refers to a measurable decline in olfactory ability that an individual is not consciously aware of. You might think, “How could I not notice if I can’t smell properly?” The answer lies in several fascinating aspects of human perception and brain function:

• Adaptation and Normalization: Our brains are incredibly adaptive. If a sensory input changes gradually or persistently, the brain can “normalize” the new baseline. If your sense of smell diminishes slowly over weeks or months, you might simply adjust to a less rich olfactory world without registering it as a deficit.
• Multisensory Integration: Our perception of flavor is not just smell; it’s a complex blend of taste (sweet, sour, salty, bitter, umami), texture, and visual cues. If you lose some ability to smell, your brain often compensates by relying more heavily on other senses. You might still enjoy the sweetness of a cake or the crunch of an apple, even if the subtle aromatic notes (like cinnamon or apple variety) are missing. This can trick your brain into thinking your smell is fine.
• Lack of Explicit Testing: Most people don’t regularly test their sense of smell. Unless prompted by a doctor or a stark incident, we rarely stop to consciously evaluate our olfactory acuity.
• Selective Deficits: Smell loss isn’t always total. Someone might lose the ability to detect subtle background odors, or specific chemical families (e.g., volatile organic compounds), while retaining the ability to smell strong, obvious scents like coffee or smoke. This partial loss can be particularly hard to recognize without specific tests.

Studies using standardized “smell tests”—like those involving “scratch and sniff” cards or odor identification kits have revealed that a significant percentage of individuals who believe their sense of smell is normal actually show measurable impairments. This phenomenon has profound implications because if you don’t know you have a problem, you can’t address its consequences.

COVID-19 doesn’t directly infect neurons responsible for smell perception. Instead, the SARS-CoV-2 virus primarily targets support cells in the olfactory epithelium (the tissue in the nose responsible for smell). These support cells express the ACE2 receptor, which the virus uses to enter cells.

1. Damage to Support Cells: When these support cells are damaged or killed, they can no longer properly maintain the delicate environment necessary for the functioning of the olfactory sensory neurons (OSNs).

2. Inflammation: The viral infection also triggers a strong inflammatory response. This inflammation can damage the OSNs themselves, disrupt the neural pathways, and even cause physical swelling that blocks odors from reaching the receptors.

3. Neural Disruption: In more severe cases, or in instances of long COVID, there can be more direct neural damage or persistent inflammation affecting the olfactory bulb (the brain structure that processes smell signals) and other brain regions involved in smell perception.

4. Persistent Issues: While the initial infection might clear, the damage to the olfactory epithelium can take months to repair. In many cases, the repair is incomplete or aberrant, leading to long-term changes like:

   • Anosmia: Complete loss of smell.
   • Hyposmia: Reduced sense of smell.
   • Parosmia: Distorted perception of smells (e.g., coffee smells like sewage).
   • Phantosmia: Smelling odors that aren’t there.

This scientific understanding helps explain why smell loss can persist and why it might be subtle, as the brain tries to reconstruct a coherent perception of smell from incomplete or distorted signals.

A diminished sense of smell might seem minor compared to other health issues, but its impact on daily life is far-reaching, affecting safety, nutrition, mental health, and social interactions.

Perhaps the most critical consequence of hidden smell loss is the increased risk to personal safety. Our sense of smell is a crucial early warning system for dangers that sight and hearing might miss:

• Gas Leaks: The characteristic odor added to natural gas (mercaptan) is often the first sign of a leak, a major fire and explosion hazard.
• Spoiled Food: The smell of rancid milk, moldy bread, or rotting meat prevents food poisoning. Without it, people might unknowingly consume contaminated food.
• Smoke and Fire: The smell of smoke can alert someone to a fire before flames are visible, giving vital time to evacuate.
• Toxic Chemicals: Many household and industrial chemicals have strong odors that signal danger, preventing accidental exposure.

Individuals with hidden smell loss might not realize they are missing these critical cues until it’s too late, placing themselves and their families at risk.

Smell is inextricably linked to flavor. Without a robust sense of smell, food becomes less enjoyable and often unappetizing.

• Reduced Appetite: When food loses its appeal, individuals may experience a reduced appetite, leading to unintended weight loss or, conversely, a reliance on highly processed foods with strong textures and basic tastes (like salt and sugar) to gain satisfaction, which can contribute to unhealthy eating habits and weight gain.
• Malnutrition: The long-term impact on appetite and food choices can lead to nutritional deficiencies, as people might avoid healthy foods that now taste bland.
• Lack of Food Safety: The inability to smell spoiled food (as mentioned above) can also lead to foodborne illness.

The emotional and psychological impact of even subtle smell loss can be profound, often leading to a diminished quality of life.

• Anhedonia: The inability to experience pleasure from previously enjoyable activities, including eating, smelling fresh laundry, or appreciating the scent of flowers, can contribute to feelings of sadness and anhedonia.
• Social Isolation: Smell plays a significant role in social bonding and personal hygiene awareness. Concerns about body odor (their own or others’) or an inability to enjoy shared meals can lead to social anxiety and withdrawal.
• Depression and Anxiety: Studies have shown a strong correlation between olfactory dysfunction and increased rates of depression and anxiety, even when the smell loss is not consciously recognized. The brain’s limbic system, which processes emotions, is intimately connected with the olfactory system.
• Loss of Memory Cues: Odors are powerful triggers for memories. Losing the ability to smell specific scents can diminish access to nostalgic memories, impacting emotional well-being.

Smell loss, even when subtle, is also increasingly recognized as an early marker for certain neurodegenerative diseases like Parkinson’s and Alzheimer’s. While COVID-related smell loss is distinct, the broader awareness of olfactory dysfunction as a neurological symptom could lead to earlier detection of other conditions.

Given its insidious nature, how can you tell if you have hidden smell loss?

• Self-Assessment (Be Honest): Actively try to smell things around you. Can you distinguish the different spices in your cupboard without looking? Can you identify the specific scent of different flowers, or the subtle aroma of a fresh rain? Pay attention to background odors you might normally ignore.
• Smell Tests: These are the most objective way. Many institutions and even online resources offer simple “scratch and sniff” tests or odor identification kits. These typically involve smelling a series of common odors and identifying them from a multiple-choice list. Even small errors can indicate a deficit.
• Consult a Doctor: If you have any suspicion, or if you had COVID-19 and haven’t had your smell formally tested, consult your primary care physician or an ENT (Ear, Nose, and Throat) specialist. They can conduct clinical olfactory tests.

While recovery rates vary, research into managing post-COVID smell loss is ongoing and promising.

1. Olfactory Training (Smell Training): This involves deliberately sniffing a set of strong, distinct odors (e.g., rose, lemon, clove, eucalyptus) for a few seconds, several times a day, over a period of months. This process acts like physical therapy for the nose, stimulating the regeneration and reorganization of olfactory pathways.
2. Omega-3 Fatty Acids: Some research suggests that Omega-3 supplements might have anti-inflammatory and neuroprotective effects that could aid in recovery, though more studies are needed.
3. Steroids (Early Stages): In the very early stages of acute smell loss (within weeks of infection), a short course of oral corticosteroids might be prescribed to reduce inflammation, but their effectiveness for chronic smell loss is limited.
4. Patience and Persistence: Recovery can be slow and gradual, sometimes taking many months or even over a year. Consistency with smell training is key.
5. Safety Measures: If you suspect hidden smell loss, take proactive safety measures:
   • Install smoke detectors and carbon monoxide detectors in your home and regularly check their batteries.
   • Be vigilant about food expiration dates and consider “if in doubt, throw it out.”
   • Be cautious with strong chemicals.