What causes persistent clear nasal discharge?

In healthy individuals, a small amount of mucus in the nasal cavity is normal; this minimal mucus serves a moisturizing and protective function for the nasal mucosa. However, when the nasal cavity is invaded by pathogens, these microorganisms stimulate the local nasal mucosa, triggering excessive mucus production.

This excessive mucus—commonly referred to as “runny nose” or “nasal discharge”—results primarily from local capillary dilation, congestion, edema, and exudation, leading to substantial leakage of tissue fluid into the nasal cavity. Persistent clear nasal discharge is most commonly associated with the following two conditions:

1. Allergic rhinitis, which causes clear, watery nasal discharge. This condition is typically accompanied by nasal congestion, frequent sneezing (often occurring in rapid succession—up to ten or more sneezes at a time), and nasal itching. Treatment requires antiallergic medications. Importantly, patients should not mistake this for the common cold and self-treat with cold remedies or antibiotics, as such symptoms are usually due to allergic rhinitis and require specific antiallergic therapy.

2. Acute rhinitis, often part of an upper respiratory tract infection—and thus part of the common cold. Patients frequently experience generalized body aches, low-grade fever, and cough. In such cases, treating the underlying cold effectively manages the acute rhinitis.

3. In certain children—or following nasal trauma—profuse clear nasal discharge may occur. In these instances, clinicians must rule out cerebrospinal fluid (CSF) rhinorrhea. If CSF leakage is suspected, prompt medical evaluation at a hospital is essential.