Why Horses With Ulcers Often Have Skin Problems — The Gut–Skin–Joint Connection

One of the most common patterns I see in horses is the combination of digestive issues and skin problems, ulcers paired with hives, itchiness, dull coat quality, or dermatitis‑like flare‑ups. Many owners treat these as separate issues, but they are deeply connected. The link between them is histamine, a natural chemical involved in both stomach acid regulation and immune responses throughout the body. When the gut becomes irritated or ulcerated, histamine production increases dramatically. The stomach contains special cells that release histamine to stimulate acid, and when the lining is damaged, these cells become overstimulated. More histamine leads to more acid, which further irritates the stomach, creating a cycle that is hard for the horse to break on their own.

But histamine doesn’t stay in the digestive tract. Once released, it circulates through the bloodstream and affects the skin, joints, and respiratory system. In the skin, histamine causes blood vessels to dilate and become leaky, which leads to hives, swelling, itchiness, and those frustrating “mystery” skin reactions that seem to appear out of nowhere. In the joints, histamine amplifies inflammation, especially when uric acid from excess protein metabolism is already present. This is why some horses with ulcers also show intermittent stiffness or joint sensitivity, the inflammation is systemic, not isolated.

Ulcers rarely exist alone. They often come with hindgut imbalance, acidosis, or dysbiosis, all of which activate mast cells and increase histamine release even further. Stress compounds the issue by weakening the gut lining and lowering the threshold for mast‑cell activation. Horses under stress, whether physical, emotional, or metabolic, produce more histamine and have a harder time regulating it. This is why a horse with ulcers may suddenly become reactive to environmental allergens, develop chronic itchiness, or show coat changes that don’t resolve with topical treatments.

The gut and skin share the same immune pathways, and both are rich in mast cells that respond to irritation, acidity, and inflammation. When the gut is compromised, the immune system becomes hyper‑reactive, and the skin becomes the easiest place for internal stress to show up. This is also why horses with digestive imbalance often have respiratory irritation, coughing, or sensitivity to dust and ammonia,  the same histamine pathways are involved. When we support the gut, we support the entire immune system. When we reduce histamine load, we support the skin and joints. And when we balance the diet, we reduce the metabolic stress that drives this whole cascade.

Understanding this connection empowers us to look beyond symptoms and address the root cause. Skin issues, joint flare‑ups, and digestive discomfort are rarely isolated problems. They are signals from the body, asking us to look deeper. When we listen to those signals and support the horse holistically, the entire system begins to settle, and the horse can return to a state of balance, comfort, and resilience.