The common causes of clear nasal discharge in the morning are: allergic rhinitis, chronic simple rhinitis, vasomotor rhinitis and so on. 1. Allergic rhinitis: when allergens are inhaled into the body, the body will produce corresponding immunoglobulin antibodies, resulting in the release of more histamine and other mediators, which in turn causes capillary dilation, increased vascular permeability, and can also cause an increase in the secretion of glands in the nasal cavity, which can lead to repeated sneezing in the morning, the flow of watery nasal discharge performance. 2. Chronic simple rhinitis: it is a chronic inflammation that occurs in the mucous membrane of the nasal cavity and the submucous layer of the nasal cavity. Due to the repeated stimulation of inflammatory mediators, it can lead to mucosal vasodilatation, increased permeability, and also cause an increase in mucous gland secretion. So the patient will appear intermittent, alternately increased nasal discharge, and mostly clear nasal discharge. 3. Vasomotor rhinitis: It is mainly induced by physical stimuli, such as changes in hot and cold air, emotional changes, intense exercise, etc., which causes non-specific release of histamine, vasodilatation, increased secretion of the glands, resulting in nasal congestion and watery nasal discharge. It is recommended to go to a regular hospital for a clear diagnosis and treatment as prescribed by the doctor for clear nasal discharge in the morning.