A broken nose (nasal fracture) frequently causes a temporary or partial loss of smell (hyposmia), or complete loss (anosmia). Although the trauma can impair this sense, the fracture itself is usually not the direct cause of the smell dysfunction. Instead, the immediate soft tissue injuries surrounding the impact typically disrupt the process of olfaction.
Why Olfaction is Impaired After Injury
The most common reason for smell loss after a nasal fracture is a physical obstruction blocking necessary airflow, known as conductive olfactory loss. This means the pathway for odor molecules is closed off, even if the sensory nerves are intact. Severe internal swelling (edema) of the delicate nasal lining is an immediate consequence of the injury, narrowing the nasal passages. This swelling prevents odor molecules from reaching the smell receptors located in the upper nasal cavity.
Trauma can also cause a septal hematoma, which is a collection of blood forming under the lining of the nasal septum, the wall dividing the nose. This pooling of blood significantly distorts the internal anatomy, further obstructing the air passage. Severe fractures may displace or deviate the nasal septum, physically impeding air movement long after the initial swelling subsides. In high-velocity injuries, almost half of patients experience post-traumatic olfactory dysfunction, which is usually attributed to these secondary soft tissue injuries.
How the Sense of Smell Works
The ability to perceive odors relies on a biological process beginning high up in the nasal cavity. To smell, air carrying odor molecules must be inhaled and directed upward to the olfactory cleft, a small area on the roof of the nasal passage. This region is lined with specialized tissue containing millions of olfactory receptor neurons. When odor molecules dissolve in the mucus, they stimulate these receptors.
The olfactory receptors transmit signals through nerve fibers that pass upward through the cribriform plate, a thin bone structure at the skull base. These fibers connect to the olfactory bulb, which processes the information before sending it deeper into the brain for interpretation. A typical nasal fracture affects the lower, more anterior part of the nose and the septum. Since the fracture site is usually far from the cribriform plate, the olfactory nerve is often protected from direct damage in less severe injuries.
When to Expect Smell to Return
The prognosis for recovering the sense of smell depends largely on the initial cause of the impairment. If the loss is due to conductive reasons, such as temporary swelling, mucosal inflammation, or blood clots, the sense of smell should gradually return as the nasal lining heals and the obstruction clears. This recovery typically happens over a period of days to a few weeks following the injury.
If the trauma was severe enough to involve the skull base, the olfactory nerve fibers passing through the cribriform plate may be stretched or torn. This results in sensorineural damage, a less common type of injury that can lead to permanent anosmia, though it is rare in isolated nasal fractures. For patients whose smell loss is a result of the more common temporary obstruction, studies show that the vast majority, around 93.9%, recover olfactory function within six months. Anyone experiencing persistent smell loss for more than a few weeks following a nasal fracture should consult a medical professional for a thorough evaluation.