Bit & Bridle

Equine Headshaking Syndrome

Other Names

  • Trigeminal-mediated headshaking syndrome (TMHS)
  • Idiopathic headshaking syndrome
  • Photic headshaking

What is Headshaking Syndrome in Horses?

Headshaking Syndrome is a painful and often debilitating neurological condition characterised by spontaneous, involuntary flicking or tossing of the head — most commonly in a vertical motion, though some horses shake laterally or exhibit a rotary movement. The behaviour is not deliberate and horses cannot be trained or disciplined out of it. Many owners initially mistake it for naughtiness or resistance, which leads to significant welfare concerns if the underlying cause goes unrecognised.

The condition can range from mild and intermittent to severe and constant, and in its worst forms renders horses unrideable. Affected horses may also rub their muzzles on their legs or on objects, snort, strike at their nose with a foreleg, and appear extremely distressed. The characteristic sensation is believed to resemble severe facial neuralgia.

Headshaking syndrome is most commonly seen in geldings and has a strong seasonal component in many cases, worsening dramatically in spring and summer. Warmbloods, thoroughbreds, and sport horses appear to be over-represented, though any breed can be affected.

Causes

The exact cause remains incompletely understood, but the majority of cases (estimated at around 60–70%) are now classified as trigeminal-mediated headshaking syndrome (TMHS). In this condition:

  • Trigeminal nerve hyperexcitability: The trigeminal nerve, which supplies sensation to the face and muzzle, becomes pathologically sensitised. This results in spontaneous, unprovoked bursts of pain — similar in mechanism to trigeminal neuralgia in humans.
  • Photic component: Bright light appears to trigger or worsen symptoms in many horses, suggesting a link between the optic and trigeminal nerve pathways. This explains the strong seasonal pattern, as light intensity and duration increase in spring and summer.
  • Hormonal factors: The condition often worsens during the breeding season, suggesting that reproductive hormones (gonadotropin-releasing hormone and sex steroids) may influence trigeminal nerve sensitivity.

Secondary causes of headshaking that must be ruled out include:

  • Dental pain or tooth root infection
  • Ear mites or otitis media (middle ear inflammation)
  • Guttural pouch disease
  • Upper airway or nasal pathology including progressive ethmoid haematoma
  • Cervical (neck) pain or musculoskeletal problems
  • Poorly fitting tack or bit problems
  • Allergic rhinitis (nasal inflammation from pollen or dust)

Symptoms and Signs

  • Involuntary, violent, or repetitive vertical head flicking, often directed downward toward the ground
  • Rubbing or swiping the muzzle against legs, fences, or the ground
  • Snorting or blowing through the nose
  • Striking at the nose with a foreleg
  • Apparent distress or anxiety, particularly during exercise
  • Sensitivity around the nose, upper lip, and muzzle
  • Worsening in bright sunlight, warm weather, or during canter and faster paces
  • Seasonal patterns — many horses are normal or near-normal in winter and become severely affected in spring and summer

Diagnosis

There is no single definitive test for TMHS; diagnosis is largely one of exclusion. Your veterinarian will typically undertake:

  • Thorough clinical examination: Including neurological assessment, oral examination, ear examination, upper airway endoscopy, and cervical palpation to rule out secondary causes.
  • Response to a nose net: Applying a fine mesh nose net that provides gentle tactile stimulation to the muzzle can relieve symptoms in many horses with TMHS. A positive response to a nose net is considered strongly supportive of the diagnosis.
  • Infraorbital nerve block: Anaesthetising the infraorbital branch of the trigeminal nerve temporarily abolishes headshaking in confirmed TMHS cases, which helps to confirm the diagnosis and indicates that the horse may be a good candidate for cryotherapy.
  • Blood tests and imaging: To rule out systemic disease, sinusitis, guttural pouch disease, or other structural causes.
  • Trial treatment: Response to medical management (cyproheptadine, melatonin) supports the diagnosis.

Treatment

There is no guaranteed cure for TMHS, but several treatments can significantly reduce symptoms in many horses:

  • Nose nets: A fine mesh net worn over the muzzle provides constant tactile stimulation to the large A-beta nerve fibres, which can suppress pain transmission in the trigeminal nerve. Approximately 50–70% of horses show improvement. Nose nets are legal in competition in the UK under British Equestrian Federation rules, though regulations vary by sport and level.
  • Cyproheptadine: An antihistamine and serotonin antagonist that has shown improvement in 50–75% of treated horses in some studies. Effects can be short-lived and the drug may cause sedation. It is not licensed for use in horses in the UK and must be prescribed off-label.
  • Melatonin: Has shown benefit in some horses, possibly by modulating the photic component of the condition. It is available over-the-counter and has minimal side effects.
  • Gabapentin: An anticonvulsant used for neuropathic pain, though poorly absorbed orally in horses and not permitted in competition. Its use is generally reserved for severely affected horses.
  • Cryotherapy (cryoneuroablation): A minimally invasive procedure in which the infraorbital nerve is frozen using cryotherapy probes under standing sedation. This temporarily abolishes sensation in the nerve and can provide relief for months to years. It is not a permanent cure — the nerve regenerates — but repeat procedures are possible and many horses achieve excellent quality of life.
  • Percutaneous electrical nerve stimulation (PENS): Electrical stimulation of the infraorbital nerve using implanted electrodes has shown promising results in research settings and is available at some specialist centres.
  • Surgical neurectomy: Permanent sectioning of the infraorbital nerve has historically been performed but is controversial due to the risk of unwanted anaesthesia of the muzzle and the potential for the condition to recur via nerve regrowth or alternative pathways.
  • Management changes: Avoiding bright sunlight (riding early morning or evening, using a dark facemask), minimising dust exposure, and reducing exercise intensity during peak season can all help manage milder cases.

Prevention

There are no proven preventive measures for TMHS, as the underlying cause is neurological and not yet fully understood. However, ensuring excellent general health — regular dental care, appropriate tack fitting, parasite control, and management of respiratory health — eliminates the secondary causes that can trigger or worsen headshaking. Early recognition of symptoms and prompt veterinary assessment prevents horses from being worked in pain for extended periods.

Prognosis

The prognosis is variable. Mildly affected horses often manage well with nose nets and management modifications, and some horses improve spontaneously after a season or two. Severely affected horses may require intensive multimodal treatment to achieve an acceptable quality of life. Cryotherapy has transformed outcomes for many horses previously considered unmanageable, with a significant proportion able to return to ridden work following the procedure. Complete, permanent resolution is uncommon in confirmed TMHS cases.

When to Call the Vet

If your horse is headshaking repetitively, rubbing its muzzle, or showing signs of facial pain — especially if the behaviour is worsening, seasonal, or associated with bright light — a veterinary examination is warranted. Early investigation helps rule out treatable secondary causes and allows treatment to begin before welfare is significantly compromised. For related conditions, see our entry on Equine Sinusitis and the equine nervous system. The British Equine Veterinary Association can direct you to specialists in this area.

Frequently Asked Questions

Is headshaking a behavioural problem or a medical one?

In the vast majority of cases, headshaking is a genuine medical condition causing real pain — not a behavioural problem. Horses with TMHS experience what is believed to be spontaneous, severe facial pain similar to trigeminal neuralgia in humans. Punishing a headshaking horse or continuing to work it through symptoms is harmful and counterproductive. Any horse showing headshaking behaviours should receive a thorough veterinary examination before any training response is considered.

Are nose nets legal in competition?

In the UK, nose nets are permitted under British Equestrian Federation rules for affiliated competitions, though riders should check the specific rules for their discipline and level. Many governing bodies have updated their rules in recent years to accommodate horses with confirmed TMHS. A veterinary certificate confirming the diagnosis is advisable. Check with your relevant national federation before competing with a nose net in place.

Will my horse always headshake?

Not necessarily. Some horses improve or fully resolve after one or two seasons — though why this occurs is not well understood. Others remain affected long-term or worsen progressively. Management and treatment can significantly reduce symptoms in many horses, allowing them to continue in ridden work. Regular review by a veterinarian familiar with the condition is recommended to assess whether treatment needs adjusting over time.

What is cryotherapy for headshaking and how effective is it?

Cryotherapy (cryoneuroablation) involves applying extreme cold to the infraorbital nerve via small probes inserted through the skin under standing sedation. This temporarily disables the nerve’s pain-conducting function. Studies and clinical experience suggest that 60–80% of horses show a significant improvement following the procedure, with effects lasting an average of 6–18 months before the nerve regenerates and symptoms may return. Repeat procedures are generally safe and effective. It is currently considered one of the most promising interventions available for severe TMHS.