Head shaking due to trigeminal irritation in horses

How do you recognise trigeminal irritation?

The most noticeable sign is a sudden, uncontrollable head movement: tossing upward, downward, or sideways. This differs from deliberate resistance to the bit. Many horses snort or blow forcefully at the same time, rub their nose on their leg or the ground, and appear momentarily panicked. The episodes last seconds to minutes and recur. In around 80 percent of cases, the condition worsens in spring and summer — which points to light sensitivity of the nerve. Riding in bright sunlight can therefore aggravate the symptoms, as can wind on the face or movement in the nostril.

Possible causes at a glance

The exact cause is not always identifiable, but a number of factors are known to play a role:

• Phototrigeminalgia: hypersensitivity of the nerve to UV light, the most common form
• Allergy or hay fever: pollen concentrations irritate the nasal mucosa and the nerve
• Dental problems or bit wear exerting pressure on nerve branches
• Middle ear problems or neck and jaw pain radiating to the trigeminal branch
• Primary idiopathic neuropathy: no clear cause found after thorough examination

Diagnosis: when should you see a vet?

Always consult a vet first if episodes recur. A proper diagnosis requires ruling out other causes such as dental problems, eye irritation, a poorly fitting saddle or bit. The vet will look at the timing (seasonal?), the context (while riding, in the field, or always?), and will carry out a neurological examination. Blood tests or allergy panels can be useful if an allergy is suspected. Record your observations in advance, preferably in the horse profile in EquiSight, so you can give the vet a complete and organised picture. Date, duration, circumstances, and frequency are all crucial details.

Treatment options and practical adjustments

There is no universal solution, but combinations of measures provide noticeable improvement in most horses:

• Nose net or fine-mesh fly mask: keeps insects and pollen at bay
• UV-protective fly mask for phototrigeminalgia
• Riding in the early morning or evening to avoid strong sunlight
• Bitless riding or switching to a softer, less contact-heavy bit
• Cyproheptadine (antihistamine): measurable improvement in around 60 percent of cases
• Melatonin supplements: help reduce light sensitivity in some horses
• Physiotherapy or osteopathy when neck or jaw dysfunction is suspected

Monitoring is essential with this syndrome

Trigeminal irritation is unpredictable: the horse may have few symptoms for weeks and then suddenly react strongly in warm, sunny weather or at high pollen concentrations. Keep a log of episodes, weather conditions, and any treatments given. In the EquiSight calendar you can record episodes and link them to notes about weather and activity. Use EquiCoach to identify patterns — for example, whether episodes are associated with specific times of day or environments. These insights help you adjust your daily routine and work with your vet to fine-tune the treatment plan.

What does this mean for sport and welfare?

Many horses with trigeminal irritation can move and work normally with good management and the right adjustments. It is important to remain honest about the horse's limits: a horse in the middle of an episode is not safe to ride. Consult your instructor and vet about what is realistic. Some owners opt for a lighter discipline or more work in an indoor arena. The welfare of the horse comes first — frequent, severe episodes without improvement warrant a reassessment of the treatment plan and sometimes of the role the horse can still fulfil.