What is the cause of excess phelgm formation in children?

Q: What is the cause of excess phelgm formation in children age 2-10 yrs even though they avoid all sorts of junk foods cold items,etc How should their immunity be boosted?

A:The collection of phlegm in the throat can be due to a variety of causes including infections of the throat, nasal passages, sinuses, upper and lower air passages and the lungs. It could also be due to allergy. Avoidance of junk foods and cold drinks can prevent it only to a certain extent. The immunity against infections can be boosted by good nutrition and vaccination against specific diseases.