Eosinophils are a type of white blood cell that usually accounts for only a few percent of the blood's leukocytes. In asthmatics, the number of eosinophils is increased in the blood. These cells invade the tissues and produce several proteins and chemicals which damage the lining of the lungs and sinuses. Often these problems are worst at night. Extremely large number of eosinophils are found in nasal polyps.
Eosinophils invade the airways in response to an insult, such as exposure to an allergen.
Sinus infection may also induce eosinophils to invade the sinus membranes. It is difficult to control asthma or sinusitis without reducing the number of eosinophils in the airway tissues. It may also be difficult to eradicate a sinus infection unless something is also done to reduce the eosinophils in the sinus membranes. The best way to eradicate eosinophils from sinus or lung tissue is with the use of steroid medications. Oral steroids work the quickest and are often given for 7 - 10 days to achieve a quick reduction in inflammation.