Normal people have very little sputum, which is mainly used to keep the respiratory tract moist. When the respiratory tract mucosa is irritated or inflammation occurs, etc., the secretions increase, resulting in more white sputum.
Common causes of white sputum include bronchitis, bronchial asthma and other respiratory diseases, as well as outside environments such as pollen, dust mites, excessively cold and hot air or irritating gases, and poor lifestyle habits such as frequent smoking, can all lead to white sputum.