Horses rear up for a range of reasons, but nearly all of them trace back to one of three root causes: pain, fear, or frustration. Rearing, where a horse lifts its front legs off the ground and balances on its hind legs, is one of the more dangerous behaviors a horse can display. Understanding what’s driving it is the first step toward fixing it safely.
Pain Is the Most Overlooked Cause
When a horse suddenly starts rearing under saddle, pain should be the first thing investigated. The behavior is essentially the horse’s way of saying it can’t tolerate what’s happening to its body. Several specific conditions are well-documented triggers.
Back Pain and Kissing Spine
The most commonly diagnosed cause of primary back pain in horses is impinging spinous processes, known as “kissing spine.” This happens when the bony projections along the top of the spine sit too close together or actually touch, creating friction and inflammation. Veterinary surveys consistently identify bucking and rearing as behaviors that owners and riders report when their horse has primary back pain. The pain intensifies when a rider’s weight compresses the spine, which explains why a horse may seem fine on the ground but become explosive under saddle. Diagnosis typically involves radiographs of the spinous processes and ultrasound of the thoracolumbar region.
Dental Problems
Dental issues are another common and frequently missed source of rearing. According to the UC Davis Center for Equine Health, rearing, head tossing, fussing with the bit, and running backward can all be dental-related. Sharp enamel points that cut into the cheeks or tongue, wolf teeth that the bit presses against, hooks forming on the cheek teeth, and even broken or misaligned teeth can make carrying a bit genuinely painful. A horse that rears specifically when asked to collect, turn, or stop is often telling you something hurts in its mouth.
Gastric Ulcers
Gastric ulcers affect a significant percentage of domestic horses, particularly those in intense training programs. Research published in Animals notes that gastric pain in horses could play a role in the development of undesired or anticipatory behaviors, and that these behaviors may persist even after the ulcers heal. A horse that has learned to associate the saddle, girth, or arena with stomach pain may rear in anticipation of discomfort before the ride even begins.
Bit Pressure and Mouth Pain
The bit itself can be a direct cause. Research comparing rein tension to pain thresholds found strong evidence that bits can cause pain-related behaviors and even lesions inside the oral cavity. One research team concluded that bits fundamentally work because they inflict considerable pain, and that horses remain functional under these conditions partly because, as prey animals, they’ve evolved strategies to suppress pain responses. A horse that rears when the rider pulls back on the reins may be reacting to genuine mouth pain, not disobedience. Harsh bits, heavy hands, or a poorly fitted bridle can all push a horse past its tolerance.
Fear and the Flight Response
Horses are prey animals. Their survival instinct is to run first and assess later. Rearing can be a fear response when a horse feels trapped and unable to flee. If the rider is holding the reins tightly and the horse encounters something frightening, it has nowhere to go forward or sideways, so it goes up. This is essentially a panic response, not a calculated act.
You can distinguish fear-based rearing from aggressive rearing by reading the horse’s body language. A fearful horse tucks its tail and turns its ears to the side. An offensively aggressive horse lashes its tail and pins its ears flat back against its head. The distinction matters because the two require very different handling approaches. Punishing a fear-based rear usually makes the problem worse by adding more stress to an already overwhelmed animal.
Frustration, Confusion, and Learned Behavior
Horses that don’t understand what’s being asked of them sometimes rear out of frustration. This is especially common in young horses being started under saddle or in horses transitioning to a new discipline with conflicting cues. When a horse receives simultaneous signals to go forward (leg pressure) and stop (tight reins), it can become confused enough to rear as a kind of overflow response.
Rearing can also become a learned behavior. If a horse rears and the rider responds by dismounting, loosening the reins, or ending the work session, the horse learns that rearing is an effective escape strategy. Over time, the behavior can persist long after the original trigger (pain, fear, or confusion) has been resolved. Research on gastric ulcers specifically notes that anticipatory behaviors may continue beyond the course of the disease, suggesting that even after a physical problem is treated, the behavioral pattern can remain.
Hormones and Stallion-Like Behavior
Rearing is a natural display behavior in stallions, often performed as part of dominance displays or breeding rituals. In the equine behavior literature, this posture is sometimes called a levade: rearing with deeply flexed hindquarters. When geldings (castrated males) display this kind of rearing, owners often suspect leftover testicular tissue is producing testosterone. But the data suggests otherwise.
A large study of over 1,200 geldings with reported stallion-like behavior found that roughly 80% had testosterone levels below the threshold that would indicate retained testicular tissue. Only about 19% had elevated testosterone. This means the vast majority of geldings that rear in a stallion-like way are doing so for behavioral reasons (learned habits, social dynamics, or training gaps) rather than hormonal ones. Blaming hormones is tempting, but it’s rarely the actual explanation.
Why Rearing Is Especially Dangerous
Rearing is considered one of the most dangerous things a horse can do with a rider on its back. Falls are the most common mechanism of equestrian injury, accounting for about 67% of all horse-related injuries in youth riders over a recent ten-year review period. An additional 2.7% of injuries involved the horse landing on the patient after a fall. When a horse rears and loses its balance backward, the rider has almost no time to react, and the horse’s full body weight can come down on top of them.
Unlike bucking, where an experienced rider can often ride through it, a rear that goes past the tipping point gives the rider no good options. Pulling on the reins during a rear actually increases the risk of the horse flipping over backward. The safest response, if it’s possible, is to lean forward, grab the mane or neck, and release the reins to encourage the horse to come back down on its own.
How to Identify the Root Cause
Because so many rearing cases start with pain, a thorough veterinary workup should come before any behavioral intervention. That means a dental exam, a back evaluation with radiographs if indicated, a gastric scope for ulcers, and a saddle fit assessment. If the horse rears only under specific circumstances (during girthing, when the bit is engaged, when weight is on its back), those patterns point directly toward a physical source.
If the vet clears the horse physically, the next step is evaluating the training and riding. Are the cues consistent? Is the rider inadvertently blocking forward movement while asking the horse to go? Is the horse being asked to do something it hasn’t been adequately prepared for? A qualified trainer who specializes in behavioral issues can often identify the gap quickly by watching the horse work.
For horses where rearing has become an ingrained habit, retraining focuses on keeping the horse moving forward. A horse that is actively moving its feet forward physically cannot rear, because rearing requires shifting weight entirely onto the hind legs. Groundwork that reinforces forward movement, combined with riding that avoids trapping the horse between conflicting aids, is the standard approach. In severe cases where the behavior poses an immediate safety risk, professional intervention is not optional.