HI, Hi, it seems that you are suffering from allergy of airways (bronchial asthma with or without allergic rhinitis/sinusitis) and most probably the white line on the back of your throat is mucus. The mucus is normally produced in the airways. It becomes thick, stringy & more in quantity in conditions of allergy & hyper-reactive airways (due to infections, dusts, fumes, cold weather etc) wherein it may trickle down from nasal region downwards on the back of throat (as post-nasal drip) and look like a white line. Use of warm saline gargles and coughing it out would help clear this line of mucus. However, other causes (such a fungal infection, or a benign or non-benign lesion) must be ruled out by thorough examination by a Pulmonologist and an ENT Surgeon. In case it persists, please get it checked by the doctor. Regards