Horse Side Vet Guide ®

Equine Health Resource

Headshaking Syndromes, Generally

Synonyms: Idiopathic, Photic, Secondary, Trigeminal Headshaking

Headshaking syndromes include ailments that results in horses repeatedly and intensely tossing their heads for no apparent reason – usually up and down, but sometimes side to side or in a circle.

Headshaking can vary in severity from mild or occasional head bobbing to violent jerks involving the entire head and neck. This behavior can be triggered by outside stimulus (or not), it can occur year round or seasonally, and it may increase in severity over time.

Chronic headshaking in horses is poorly understood and causes frustration for horse owners and veterinarians. A variety of studies have failed to definitively identify the cause of this behavior and more research is needed.

Strictly speaking, headshaking is not a diagnosis but a sign of another underlying problem or disease. There is a whole subset of horses that shake their heads, for whom no other evidence of disease can be found. Horses in that group can be called “primary” headshakers versus those for which disease or injury in another body system can be proven, resulting in “secondary” headshaking. Idiopathic (“of unknown cause”) headshaking are cases that cannot be attributed to an underlying cause with veterinary diagnostic testing.

It is important to know that headshaking behavior in ridden horses often relates to training and rider problems, and less commonly to discomfort from ill-fitting tack or dental conditions.

Similarly, headshaking in horses that are not under saddle sometimes results from diseases associated with different body systems; guttural pouch problems, external and internal ear problems, pain from ill-fitting tack, oral and dental problems, even skull and neck injuries.

Photic head shaking may be triggered by bright light. When these horses are led into bright sunlight from darker environments, head shaking starts and can be violent and persistent. The severity may vary, depending upon many factors and is graded by vets on a scale of 1-5.

Trigeminal headshaking is the term used when this behavior is thought to be caused by inflammation of the trigeminal nerve, which is responsible for skin sensation on the face. In these cases, sensory nerve irritation brought on by light, wind, cold, touch or other external factors is thought to cause a tingling or burning sensation in the facial skin. It is difficult to separate this syndrome from photic headshaking, except that not all cases of trigeminal headshaking worsen during exposure to light.

Other studies suggest that this behavior is caused by residual viral presence and inflammation following a viral infection. Others postulate that trauma or hormonal changes bring on this behavior.

The key to diagnosing and treating headshaking syndromes is to rule out all of the other more obvious causes of irritation that could result in this behavior. If all other possible causes are excluded we are left with idiopathic or photic headshaking as the diagnosis.  

Treatment is focused on resolving the underlying cause. In cases where no underlying cause can be identified, there are several medications (carbamazepine and cyproheptidine) that have shown some therapeutic value in some horses. Nose nets and face masks may help in some cases of the photic syndrome. In severe cases, surgery may be recommended to sever certain nerves that supply sensation to the muzzle and face.

Prognosis & Relevant Factors

The prognosis is fair with treatment but always depends on the specifics of the particular condition and the particular horse. In photic and trigeminal headshaking, some medications may improve the behavior.

The prognosis for secondary head shaking depends on success of treating the underlying condition.


  • What possible causes of this behavior have you ruled out?
  • What is the latest research on head shaking?
  • Many products are claimed to cure or lessen head shaking, what do you think?

    Prevention of secondary head shaking depends on the treatment of the underlying disorder.

    Application of fly masks or nose nets may help lessen this behavior in some horses. Some horses with the photic syndrome may benefit from management changes that keep them out of bright sunlight.

    Helpful Outside ResourcesCredible Equine Health Information on the Internet

    Author: Doug Thal DVM Dipl. ABVP


    Higgins AJ, Snyder JR eds. The Equine Manual. 2nd Ed. Edinburgh: Elsevier Saunders 2006.Madigan JE, Bell S. Evaluation and Treatment of Headshaking. AAEP Proceedings, 1997 43:340-42.


    We're not around right now. But you can send us an email and we'll get back to you, asap.