The phenomenon of light phlegm is often caused by viral infection of the respiratory system. When a virus invades the respiratory system, it causes an inflammatory reaction in the mucous membrane of the respiratory tract and secretes a large amount of inflammatory exudate. In addition, the eosinophils or phagocytes in the body also tend to gather at the site of inflammation, engulfing foreign viruses, followed by the shedding and necrosis of these cells, and inflammatory exudates mixed together, easy to form the phenomenon of clear sputum, often using antiviral drugs for treatment, the effect is very good, such as Pu Di Lan anti-inflammatory oral solution, four seasons antiviral combination or Blue Scutellaria oral solution, the effect of oral administration are is relatively good, need to take 3 times a day, take 3-5 days in a row, the effect will be better. If allergies occur, it will also lead to the symptoms of clear sputum, this time you need to use anti-allergy drugs to treat, such as loratadine or cetirizine hydrochloride.