Any irritating substances left in this area will cause inflammation and swelling that can be seen externally. A large accumulation in this area can also cause swelling, as well as painful urination. Contrary to popular belief, however, smegma accumulation will not block the ability of a horse to urinate. These conditions are not life-threatening, but a swollen sheath needs to be cleaned. This is best accomplished under sedation by a veterinarian.
Sedation calms the horse, allows the penis to drop, and facilitates visual inspection of the area.
Careful inspection is important, since, rarely, the swelling is caused by a tumor that must be treated in a timely manner. Many owners choose to clean their horse's sheath themselves. No harm can come from this practice as long as all irritating substances are rinsed from the area after it is cleaned. Mild soap can be used, as well as any dish soap. All soaps are irritating and must be rinsed thoroughly.