Seborrhea is a chronic skin condition that causes excessive scaling and greasiness of the horses skin and coat. It occurs as three different presentations--dryness, excessive greasiness, or scaling and greasiness with local or diffuse inflammation of the horse's skin and haircoat.

Seborrhea is almost always a secondary result from a primary disease, it is rarely a primary disease. The most common primary diseases which cause seborrhea are systemic diseases (pemphigus foliaceus, equine sarcoidosis, liver disease, nutrition deficiencies, tumors, intestinal malabsorption, toxicosis or imbalances), ectoparasites, bacterial or fungal diseases, and immune-mediated skin conditions. Application of topical products and being stabled with heating can also cause seborrhea.