What is the most common cause of acute sinusitis?

The most common cause of acute sinusitis is viral upper respiratory infections. These infections, such as the common cold, frequently lead to inflammation of the sinuses. When the nasal passages become inflamed and congested due to a viral infection, the normal drainage of mucus from the sinuses can be impeded, creating an environment conducive to the development of sinusitis.

Acute sinusitis often progresses after a viral upper respiratory infection, as the initial viral infection triggers sinus inflammation. While bacterial infections can occur following the initial viral infection, they are not the primary cause of acute sinusitis. In fact, many episodes of sinusitis resolve without the need for antibiotics, indicating that the initial viral infection is responsible for the majority of cases. Fungal infections are more associated with chronic or complicated sinusitis and are much less common in acute presentations. Environmental allergens can contribute to sinus issues, but they are not a direct cause of acute sinusitis as they do not typically result in the same inflammatory cascade triggered by viral infections. Thus, viral upper respiratory infections stand out as the leading cause of acute sinusitis.