The SARS-CoV-2 virus, which causes COVID-19, frequently targets the upper respiratory system, making the sinuses and nasal cavity a common site of infection and symptom manifestation. Nasal and sinus involvement has been a highly prevalent feature across various viral variants, often presenting with symptoms that closely mimic a common cold or seasonal allergies. This overlap makes it difficult to initially distinguish COVID-19 from other common ailments. Understanding the specific biological mechanisms and the symptom profile of the infection in the upper airways is important for recognizing the disease, as the nasal cavity is often the initial entry point for the virus.
How SARS-CoV-2 Impacts Nasal Tissues
The virus gains entry into human cells by binding its spike protein to the Angiotensin-Converting Enzyme 2 (ACE2) receptor. This receptor is abundant on the epithelial cells lining the nasal cavity, making this area a primary site for initial viral replication. The entry process is facilitated by the enzyme transmembrane protease serine 2 (TMPRSS2), which is also highly expressed in these cells. The co-expression of ACE2 and TMPRSS2 creates a gateway that allows SARS-CoV-2 to efficiently infect the tissue.
In the olfactory region, the virus targets ACE2 receptors found on supporting cells (sustentacular cells), rather than the olfactory sensory neurons themselves. Infection of these non-neuronal supporting cells initiates a localized inflammatory response, which is the direct cause of most nasal and sinus symptoms. This inflammatory reaction, termed rhinitis, leads to swelling and irritation of the nasal lining. The primary issue is this direct viral-induced inflammation, though secondary bacterial sinusitis can occasionally develop as a complication.
Common Sinus and Nasal Symptoms
The localized inflammation caused by the virus results in a spectrum of familiar upper respiratory symptoms. Patients frequently experience nasal congestion and rhinorrhea (a runny nose), characterized by a watery or mucoid discharge. Inflammation within the sinuses can also produce facial pressure or pain, often described as a headache or a feeling of fullness across the cheeks or forehead. These symptoms collectively create a presentation similar to acute sinusitis.
The most distinctive nasal symptom associated with COVID-19 is the abrupt onset of anosmia (the complete loss of the sense of smell). This is often accompanied by ageusia (the loss of taste), as taste perception is heavily reliant on smell. Unlike the smell loss seen in a common cold, which is usually due to physical blockage from congestion, COVID-19-related anosmia can occur suddenly and often without significant nasal obstruction. While acute COVID-19 symptoms typically last one to two weeks, the loss of smell may be one of the earliest signs, sometimes appearing before other symptoms, and can persist longer than the general respiratory symptoms.
Distinguishing COVID Sinus Symptoms from Allergies or Colds
Differentiating COVID-19 from seasonal allergies or the common cold is often difficult, but certain symptom characteristics provide clues. Seasonal allergies are marked by intense itching of the nose, throat, and eyes, and often include profuse, watery rhinorrhea. Systemic symptoms like fever, muscle aches, or fatigue strongly suggest a viral infection, such as COVID-19, as these are rarely features of allergic rhinitis. Allergy symptoms also tend to follow a predictable seasonal pattern and improve with antihistamine medication.
When comparing COVID-19 to a common cold or flu, the defining characteristic is the nature of the smell loss. A cold or flu may cause a reduced sense of smell (hyposmia) due to heavy nasal congestion, which physically prevents odors from reaching the olfactory receptors. In contrast, COVID-19 often causes a complete loss of smell (anosmia) that can occur abruptly, even without a significantly stuffy nose. The common cold generally does not cause the severe body aches or high fever frequently reported with COVID-19. Therefore, the combination of systemic symptoms and the sudden, complete loss of smell serves as a strong indicator that the illness is likely COVID-19.
Lingering Upper Respiratory Effects
For many people, the effects of the virus on the olfactory system persist long after the acute infection has resolved, becoming a component of post-acute sequelae, often called Long COVID. Persistent anosmia, a smell loss lasting weeks or months, is a common complaint that substantially affects quality of life, including appetite and food enjoyment. A related long-term effect is parosmia, where odors are perceived as distorted or unpleasant, with common smells like coffee or meat registering as foul or chemical.
This ongoing olfactory dysfunction may affect more than ten percent of COVID-19 patients for prolonged periods. This lingering issue is thought to result from a protracted inflammatory state or a failure of the supporting cells in the olfactory epithelium to fully recover and regenerate. In some cases, chronic post-viral inflammation, known as chronic rhinosinusitis, may develop and persist for months after the initial illness, leading to ongoing congestion and facial discomfort.