Sinus problems occur when sinuses become clogged or infected. Sinuses are air-filled cavities surrounding the nose and under the eyes. There are 4 types of sinuses around the nose. The air inside the sinus cavities helps resonation of the voice. The sinus cavities themselves help to lend shape and strength to the bone around the nose. Sinus problems often result due to the infection of these cavities due to attack from pathogens that could be bacteria, virus, or allergens. Most sinus problems happen when mucus drainage doesn't take place effectively. The mucus drainage which flows down under gravity is clogged due to a variety of reasons.
When the nasal passages are infected from sinus problems and there is inflammation, it can lead to influx of cells intended to help immunity. It also causes the mucus lining to swell as a response to the pathogens. This increases the secretion of mucus which might be slightly thicker as well. The increased and thickened mucus could lead to clogging of the sinus cavities causing breathing problems, stuffiness and congestion. In a few hours, the clear mucus could turn into green and then yellow showing the response to increased bacterial attack.
The nasal passages are nutrient rich and clogging of the nasal passages provides the right kind of warm and moist conditions for increased bacterial growth. Bacteria and fungi increase exponentially feeding on the live cells of the mucous lining and further aggravating the situation. Sinus problems can have many implications some serious and some not quite. However, it is always advisable to consult a doctor as soon as possible.
One of the most important consequences of sinusitis is facial swelling and pain in the cheekbones, toothache, headache and burning sensation in the nasal linings coupled with blood streaked mucus sometimes. Sinusitis can grow into a major problem whereby the infection may spread through the sinus wall into the brain causing a fatal problem like meningitis or brain abscess. Since nasal cavities are closely located to brain, eyeballs and skull, infection can spread very quickly. If it spreads to the skull it can cause osteomylitis.
Infections around the eye are called orbital cellulitis. Other problems caused by sinusitis include a pus like discharge which is caused by increased struggle between the immune cells and the pathogens.
Infection of the mucus linings can also result in overgrowth of the underlying tissue resulting in nasal polyps. These nasal polyps further reduce the space inside the nasal passage resulting in more clogging. The increased surface area provided by turbinates or cartilage folds inside the nasal passage can prove to be a disadvantage during sinusitis. If the nerve cells are malfunctioning the expansion of blood vessels to provide increased blood supply might be inconsistent resulting in clogging of one of the nasal passages. The sinus cavity  is very small and it is easy to get clogged due to mucus build up.
Temperature changes and pressure alterations can cause sinus infection too. This can result in post nasal drip with excess mucus dripping out of the nose. The anatomical features of the nasal area along with certain hereditary conditions can also result in sinusitis. Often the cartilarge nasal septum which divides the passage into two parts can be bent or crooked resulting in uneven spaces. This can push the turbinate folds and put pressure on it effecting the nerve cells further and causing increase clogging.