What is the primary cause of sinusitis?

The primary cause of sinusitis is often an upper respiratory infection (URI). This is because a URI can lead to inflammation and blockage of the sinus cavities, resulting in the accumulation of mucus and the development of sinusitis. Viral infections, such as the common cold, are most commonly associated with URIs and can trigger sinusitis by causing swelling in the nasal passages, obstructing normal drainage from the sinuses.

In contrast, although allergic reactions may contribute to sinus inflammation, they are not the primary cause. Similarly, exposure to pollutants can irritate the nasal passages but is also not a main cause of sinusitis. Cold weather can exacerbate symptoms or increase susceptibility to infections, but it does not directly cause sinusitis. Thus, understanding the connection between URIs and sinusitis is crucial for recognizing the condition's primary trigger in most cases.