A sarcoid is a kind of tumor (abnormal cell growth), that commonly occurs on horses and is thought to be caused by a virus, likely the bovine wart (Papilloma) virus. Although multiple sarcoids can occur on the same horse, they do not metastasize or spread in the same way as tumors.

Most sarcoids are benign, flat, crusty grayish growths that do not change rapidly in appearance or size. More aggressive sarcoids (called fibroblastic) tend to have a raised bumpy reddened surface, they may bleed easily, and they can grow rapidly. Common locations for sarcoid are the ears, around eyes and muzzle, and around the sheath, but they can appear anywhere.

In typical cases of slow growing or benign sarcoids, you should monitor the size and shape on a regular basis and have your vet advise on them during routine healthcare appointments. In most cases, you will want to remove them. Your vet will discuss the options for treatment and the associated costs. If there is a major or sudden increase in their number or growth rate, or they become large enough to interfere with bodily functions, treatment becomes more urgent.

Different vets will have different ways of managing the problem. In general, the larger the sarcoid, the more aggressive and expensive the treatment. Sarcoids around the eye are problematic because there is little tissue to work with and there is the added concern of the treatment causing eye damage.