Sarcoids are the most common skin tumour in horses and ponies and, although they may look like warts, they are locally destructive and are a form of skin cancer.
They are most often found on the abdomen, inside the back legs, around the sheath, on the chest and around the eyes and ears. They also often appear at the site of old scars, particularly on the legs. These are sites where flies typically congregate and insect transmission may be involved in the development of the condition.
Young to middle-aged horses are most commonly affected and there may be a genetic predisposition. It is a condition that is unique to horses. There is no clear link between colour or breeds of horses being more susceptible.
Sarcoids can appear singly as tiny lumps or in clusters. As they enlarge, the skin may ulcerate and become infected. In summer, they attract flies and can end up as open sores that will not heal.
The appearance of sarcoids can vary considerably. In the early stages they may appear innocuous and are sometimes missed completely if they are concealed within the horse’s coat.