The sinuses are hollow recesses in your skull that are lined with mucous membranes. This mucous normally drains into the nasal passageways and out of the nose or into the back of the throat (and is swallowed), but when conditions such as a cold virus cause excess mucous or inflammation of the mucous membranes, this process may be impaired. The sinuses can become clogged and air flow to the sinus cavities can be impeded. These conditions are ideal for bacteria to grow in. This is how the common cold virus can lead to a bacterial sinus infection. Your immune system may already be tired from fighting the cold virus which makes it easier for a bacterial infection to start and progress.
Many people mistake sinusitis for a bad cold, which is understandable when you know that most cases of sinusitis start out as a simple cold and only progress to sinusitis later on.
You can prevent a cold from turning into a sinus infection by drinking a lot of water to keep your mucous thin and watery so that it can drain easier. Using a cool mist humidifier may also help to keep your mucous thin. Some medical professionals also recommend that you take a decongestant type medication when you have a cold to prevent a sinus infection. Examples of decongestants include pseudoephedrine and nasal sprays such as Afrin (oxymetazoline). Flying in an airplane when you have a cold may increase your risk of developing sinusitis. Additionally, if you have a bad cold or sinus infection and get on an airplane or engage in other activities that involve significant changes in altitude, you may be at risk for developing barotrauma of the ears or sinuses.
Some studies have shown that using a neti pot (nasal irrigation) may decrease the number of sinus infections a person has. However, at least one study has had opposite results, showing that using a neti pot actually increases your risk of developing sinusitis.Treatment
Once a cold develops into acute sinusitis you need to be treated with antibiotics. Prolonging treatment when your cold symptoms include facial pain and pressure, headaches, toothaches or other symptoms of sinusitis will likely only prolong your suffering.Fungal Sinus Infections
It is also possible for your sinuses to become infected with a fungus. Fungal sinus infections often become chronic and can be difficult to treat. A sinus infection is considered chronic when symptoms last three months or longer. Fungal infections may require sinus surgery to resolve. Sinus surgery is performed using an endoscope, a long tube with a tiny camera on the end of it. When the endoscope is inserted through the nose, the surgeon can see inside of the sinuses and will "clean" out the sinus cavities. Infectious material, excess mucous, any damage or diseased tissue, or abnormal growths such as nasal polyps are removed. Once the sinuses are clear and draining again any remaining infection will often resolve on its own.
American Academy of Allergy Asthma and Immunology. Sinusitis. Accessed: December 26, 2012 from http://www.aaaai.org/conditions-and-treatments/library/At-a-glance/sinusitis.aspx
American Academy of Otolaryngology Head and Neck Surgery. Sinusitis. Accessed: December 26, 2012 from http://www.entnet.org/HealthInformation/Sinusitis.cfm
National Institute of Allergy and Infectious Diseases. Sinusitis. Accessed: December 26, 2012 from http://www.niaid.nih.gov/topics/sinusitis/Pages/cause.aspx
Pubmed Health. Sinusitis. Accessed: December 26, 2012 from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001670/