It can be a side effect of crying, exposure to cold temperatures, cocaine abuse,[3] or drug withdrawal, such as from methadone or other opioids.

Some causes of rhinorrhea include: acute sinusitis (nasal and sinus infection), allergies, chronic sinusitis, common cold, coronaviruses (COVID-19), decongestant nasal spray overuse, deviated septum, dry air, eosinophilic granulomatosis with polyangiitis, granulomatosis with polyangiitis, hormonal changes, influenza (flu), lodged object, medicines (such as those used to treat high blood pressure, erectile dysfunction, depression, seizures and other conditions), nasal polyps, non-allergic rhinitis (chronic congestion or sneezing not related to allergies), occupational asthma, pregnancy, respiratory syncytial virus (RSV), spinal fluid leak, and tobacco smoke.

Cold-induced rhinorrhea occurs due to a combination of thermodynamics and the body's natural reactions to cold weather stimuli.

[13] Over the course of a viral infection, sinusitis (the inflammation of the nasal tissue) may occur, causing the mucous membranes to release more mucus.

[14] Rhinorrhea can also occur when individuals with allergies to certain substances, such as pollen, dust, latex, soy, shellfish, or animal dander, are exposed to these allergens.

In people with sensitized immune systems, the inhalation of one of these substances triggers the production of the antibody immunoglobulin E (IgE), which binds to mast cells and basophils.

IgE bound to mast cells are stimulated by pollen and dust, causing the release of inflammatory mediators such as histamine.

Particulate matter in polluted air and chemicals such as chlorine and detergents, which can normally be tolerated, can make the condition considerably worse.

[18] Other causes include cystic fibrosis, whooping cough, nasal tumors, hormonal changes, and cluster headaches.

Rhinorrhea can also be the side effect of several genetic disorders, such as primary ciliary dyskinesia, as well as common irritants such as spicy foods, nail polish remover, or paint fumes.

Though blowing may be a quick-fix solution, it increases mucosal production in the sinuses, leading to frequent and higher mucus buildups in the nose in the medium term[citation needed].