One of the most bothersome things about being sick or having seasonal allergies is that it makes your nose stuffy and blocked. Even when you aren't sick, perhaps you've noticed that when you take a deep breath, only one of your nostrils seems to be allowing the air in.
What you're experiencing is actually a normal bodily process. Multiple times a day, without us even noticing, the nostrils naturally switch between a dominant nostril for airflow. This process is called the nasal cycle. The body actually switches the dominant nostril as frequently as every two hours while we're awake. This switch is less frequent when we're sleeping.
During the congestion phase, one nostril will experience reduced airflow, while the opposite nostril will be open, or decongested, allowing for more air to pass through it. The decongested phase actually fatigues the open nostril, as air dries it out and brings pathogens into contact with it. This is why it's important for the dominant nostril to swap. This alternating cycle is automatic, regulated subconsciously by the hypothalamus in the brain.
The nasal cycle is important for a number of reasons. First, it protects the lining of the nose and respiratory system. Having the dominant nostril alternate reduces the risk of damage and also makes it easier for the nasal passage to protect against pathogens. The nose also has to rest and repair. Air exposure dries it out – so without time to recuperate, this could make it easier for pathogens and inflammation to cause damage. Part of the congestion process also sees increased blood flow to the nose's vessels. This ensures the nostrils are moistened properly for both the repair and recovery processes, and so that air is warmed and moistened as it passes through the nostril.
A number of things can affect the nasal cycle's normal function. Respiratory conditions such as colds and flu result in an increase in mucous production. This restricts how easily the nasal passages are able to alternate. Allergens such as pollen or dust mites can cause severe inflammation of the nasal tissues. Certain medications, such as those for high blood pressure, can cause irritation of the nasal lining, too. Overuse of nasal decongestants can cause rhinitis medicamentosa.
For others, structural issues interfere with their nasal cycle. Nasal polyps are an outgrowth of the nasal lining that usually occurs in both nostrils. A deviated nasal septum – where the cartilage and bone plate between the nostrils is off-centre – can also make the nostrils feel constantly congested or blocked.
If you're struggling with blocked nostrils, infections such as colds and the flu are usually the most common culprits. But if you find one nostril is persistently blocked for more than two weeks, it's usually a good idea to get it checked out.