CONDITION
Facial Nerve Paralysis
Facial nerve paralysis describes a loss of normal movement on one side of the face, caused by disruption to the nerve that controls the muscles of facial expression. The facial nerve also carries fibres responsible for tear production and some aspects of taste, so changes in these functions can occur alongside the visible asymmetry. Owners often notice that one side of the face appears drooped or slack, that the ear on the affected side hangs lower, or that the eye on that side does not blink normally. Drooling from one side of the mouth, difficulty holding food, or a change in the shape of the muzzle when the dog or cat is at rest may also prompt concern. In some cases the onset follows an ear infection or head trauma, but in many animals no clear trigger is identified. This page explores the patterns that suggest facial nerve involvement, the mechanisms that can disrupt the nerve's function, the investigations used to clarify the picture, and the range of approaches taken when managing the condition and its effects.
Why this matters now
Facial nerve paralysis can appear at any age, though idiopathic cases—those without an obvious cause—tend to occur more frequently in middle-aged to older dogs. Certain breeds, including Cocker Spaniels, Boxers, and English Setters, appear over-represented in some case series, though the condition is documented across all breeds and in cats. In younger animals or those with a recent history of ear disease or head injury, the onset may follow a clear precipitating event, whereas in many mature animals the paralysis develops without warning.
The onset is often sudden, with the full extent of facial asymmetry apparent within hours to a few days. In some animals the deficit remains stable from that point, while in others there may be subtle worsening over the first week before a plateau is reached. Recovery, when it occurs, tends to unfold over weeks to months and may be incomplete, leaving residual asymmetry or altered function. A minority of animals experience recurrence on the same side or, less commonly, later involvement of the opposite side.
Signals & patterns
Early signals
Ear position asymmetry
The ear on the affected side may hang lower or appear less mobile than the other, particularly noticeable in breeds with erect or semi-erect ears. In dogs with naturally drooped ears the change can be more subtle but may be evident when the dog is alert or moving.
Incomplete eye closure
The eyelids on one side may not meet fully when the animal blinks, or the blink may be absent altogether. Owners sometimes notice the eye appearing wider or more exposed, and the surface of the eye may begin to look drier or duller within the first day or two.
Lip droop on one side
The corner of the mouth on the affected side may sag, and saliva can accumulate or drip from that side, particularly after drinking. Food may also be more difficult to hold on the affected side, leading to messier eating or preferential chewing on the opposite side.
Nostril flare asymmetry
When the dog breathes, the nostril on the affected side may appear less active or fail to flare in the usual way. This is most apparent during exertion or panting, when the normal nostril moves more obviously.
Later signals
Dry or inflamed eye surface
Without normal blinking and tear distribution, the cornea on the affected side can become dry, cloudy, or develop a discharge. In some cases the surface may develop erosions or ulceration if the protective mechanisms remain impaired for days to weeks.
Muzzle deviation at rest
Over time, the lack of muscle tone on the paralysed side may cause the muzzle to appear pulled towards the normal side when the animal is relaxed. This becomes more pronounced as any compensatory muscle use on the unaffected side continues.
Persistent head tilt
In cases where the facial nerve involvement is part of a broader disturbance affecting the inner ear or vestibular apparatus, a persistent tilt of the head towards the affected side may develop or persist beyond the initial onset.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
Last reviewed: Invalid Date ·