Sinuses are hollow, air-filled cavities, located behind the cheekbones and the forehead. There are four different types of paranasal sinuses - maxillary sinuses, frontal sinuses, ethmoid sinuses, and sphenoid sinuses. All these sinuses are lined by a soft tissue known as the mucosa. Sinusitis refers to an inflammation of the lining of the paranasal sinuses, which can be caused by several factors, including common cold, viral or bacterial infections, nasal polyps, allergies, fungal infections, or a deviated septum. Swelling or inflammation can block the sinuses and cause an accumulation of fluid or mucus inside them. This can create a favorable environment for the growth of harmful microorganisms that can eventually cause infections. Sinusitis is usually classified into four major types - acute sinusitis, chronic sinusitis, subacute sinusitis, and recurrent sinusitis. However, there is another classification based on the type of sinus affected. All these various types of sinusitis are discussed below. Acute sinusitis is marked by a sudden onset of cold-like symptoms that usually resolve within 1 to 4 weeks. It is often caused by a recent episode of upper respiratory tract infection. Acute sinusitis can be further classified into acute bacterial and viral rhinosinusitis. Out of these two subtypes, viral rhinosinusitis is more prevalent. Acute sinusitis can produce several symptoms like headache, throbbing facial pain, a runny or stuffy nose, fever, a reduced sense of smell, pressure and tenderness around the eyes, nose and cheeks, and bad breath (halitosis). If the aforementioned symptoms of sinusitis last for 4 to 12 weeks, then it is classified as subacute sinusitis. The symptoms of subacute sinusitis can be less severe as compared to the symptoms of acute sinusitis. Sometimes, subacute sinusitis can be a transition between acute and chronic rhinosinusitis. If the symptoms of sinusitis last for more than 12 weeks or 3 months, it is considered as chronic sinusitis. Chronic sinusitis may be caused by infections, but is more commonly associated with nasal polyps and a deviated nasal septum. Nasal polyps are noncancerous growths or polypoidal masses that develop in the mucous membrane of the nasal passages and sinuses. Sometimes, an allergy to certain types of fungus, or fungal infection of the sinuses can also cause chronic sinusitis. Accordingly, it is subdivided into three types, known as chronic rhinosinusitis without polyps, chronic rhinosinusitis with polyps and allergic fungal rhinosinusitis. Out of these, chronic rhinosinusitis without nasal polyps is the most common. The symptoms of chronic sinusitis are similar to acute sinusitis symptoms. Recurrent sinusitis refers to several episodes of acute sinusitis in a single year. This condition is more common among individuals with allergies and asthma. As mentioned already, there are four types of paired paranasal sinuses in our body. Sometimes, sinusitis is classified into four types depending on the particular type of sinus that is affected. Maxillary Sinusitis - The maxillary sinuses are located behind the cheekbones and they are the largest paranasal sinuses. Maxillary sinusitis can cause pain and pressure in the maxillary area, and swelling around the eyes and cheeks. It can also cause headaches. Ethmoid Sinusitis - The ethmoid sinuses are present in the upper part of the nasal cavities and the orbits. An inflammation or infection of these sinuses can cause headaches, sore throat, reduced sense of taste and smell, and swelling and pain around the eyes. Frontal Sinusitis - The frontal sinuses are located in the forehead. An infection or swelling of the frontal sinuses can produces symptoms like headache and pressure or tenderness around the eyes. Sphenoid Sinusitis - Sphenoid sinusitis is relatively rare. These sinus cavities are located behind the ethmoid sinuses and above the nasopharynx. Sphenoid sinusitis can produce a vague and dull headache, and pain and tenderness behind the eyes. Sinusitis can be managed with saline nasal sprays and decongestants. Pain relievers such as aspirin and acetaminophen are usually prescribed to relieve the headache and facial pain caused by sinusitis. Sometimes, corticosteroids are also recommended for sinusitis treatment. Antibiotics are usually used for severe sinusitis caused by bacterial infections, while sinusitis caused by fungal infections can require the administration of antifungal medications. Similarly, if sinusitis is associated with allergies, then allergy shots can prove helpful in treating this condition. Sometimes, surgery can also be required for treating and preventing the recurrences of sinusitis, especially if it is associated with nasal polyps. Apart from these, some simple home remedies like application of a warm compress on the face, and steam inhalation can help relieve sinusitis symptoms. Thus, there are several different types of sinusitis, depending on the severity and duration of the symptoms, and the type of sinus affected. However, the symptoms of all types of sinusitis are more or less similar. Therefore, physicians can perform certain tests, such as a nasal endoscopy, a nasal and sinus culture, and an MRI CT scan, along with a physical examination of the nasal passages in order to find out the actual cause of sinusitis. Disclaimer: This article is for informative purposes only, and should not be treated as a substitute for professional medical advice.