Short-term blockage
A cold or a flare of allergy can close the nose for days or weeks and then ease.
Blockage that stays
A septal deviation or ongoing sinus disease is more likely if one side is always worse. That is an ENT question, not something to decide from a mirror.
Reviewed by the Sachi Hospital medical team · September 2026. This is general education, not personal medical advice. Related service: Deviated nasal septum.