Sarcoids are a type of benign skin tumour which are prevalent in horses and donkeys. They are very variable in their appearance but an experienced vet can usually differentiate them from other types of skin lesion.

In many cases they cause few problems although they are unsightly and attract flies if ulcerated. However, if they become very numerous, rub on tack or invade sensitive areas such as the eyelids they can be very problematic.

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matrix of four images showing equine sarcoids

What causes them?

Sarcoids are caused by infection with a virus caused Bovine Papilloma Virus (BPV). Although this virus originated in cattle at some time in its evolution it is unlikely that infection from cattle plays a role any more. Most horses become infected with BPV at some time in their lives although most will not develop sarcoids - that depends on their own individual susceptibility. BPV is believed to be spread by biting flies.

Typical Appearance

Sarcoids are mostly (but not always) restricted to specific areas of the horse. Typical areas are from the tail beneath the back legs, along the midline of the belly, between the front legs and around the head, particularly the eyelids. They occur in several different forms as described below although many lesions can be intermediate between the different types.

Occult Sarcoids

These are flat, hairless, lichen-like, slightly dry and crusting, dark patches. They often have a smooth, dark hairless area around them. They are most common on the inside of the upper limbs, the neck and around the eyes.

Verrucose Sarcoids

These are raised, knobbly, dark areas that often spread into poorly defined margins. They can also be ulcerated on occasions.

Nodular Sarcoids

These are firm and nodular skin lumps which may have normal skin over them.

Fibroblastic Sarcoids

These are ulcerated, weeping, raised sore lesions that may develop a stalk and become cauliflower-like. They can develop in any site.

Mixed Sarcoids

Sarcoids are commonly a mixture of two or more of the forms described above.

Malevolent Sarcoids 

These are rare, invasive sarcoids that invade deeper tissues beneath the skin.

Location, Location, Location!

A small sarcoid in an area which has plenty of loose skin and does not rub on tack is easier to treat and less problematic than a sarcoid in more sensitive areas. Particular problems are sarcoids around the eyes, on the ears, at the corners of the lips where a bit rubs and on the girth line. These need aggressive treatment whilst still small. It is especially important to treat sarcoids around eyes before they enlarge.

Is the lump on my horse a sarcoid?

Although experienced equine vets are good at spotting sarcoids, a definitive diagnosis can only be made by looking at a biopsy, or tissue sample, under the microscope. This needs to be sent off to a laboratory. However taking a biopsy without removing the entire sarcoid can make it more aggressive so in most cases we start treatment based on the location and character of the lesions.

Possible treatments

There are many different treatments for sarcoids. Where a condition has many different treatments it means that none of them are completely satisfactory - we help you chose which treatment is best based on the location, number and type of the lesions.

Banding with rubber rings

Banding is a very satisfactory treatment where the sarcoid has a distinct neck or stalk - it is cheap and has a high success rate. Unfortunately it is not suitable for sarcoids which have no "neck". In general, if a ring can go over the whole sarcoid without coming off, it is the first line of treatment. We often use lamb castration rings but sometimes use larger rubber bands.

Freezing with liquid (cryosurgery)

We use liquid nitrogen for treating many sarcoids. It is best used for treatment of flat sarcoids and less successful for deep ones. 

Topical medication

In some cases we recommend application of topical treatments. Often because of the location or type of lesion. These can include drugs such as:
Imiquimod or "Aldara", an immune response modifier.
Tazarotene or "Zorac", a topical retinoid used for treating psoriasis in people.
XXterra, an ointment which contains an extract of Sanguinara canadensis.

Chemotherapy drugs, applied as a cream onto the sarcoid

This can be an effective treatment for some sarcoids. We use a cream supplied by the University of Liverpool and need to take photos of the sarcoids in order to apply for a supply of cream.  Although it has a good success rate, it is a relatively expensive treatment and requires at least 3 visits. It is not suitable for all sarcoids, particularly those where the cream will be easily rubbed onto other sensitive tissues. The active ingredients in the cream are dangerous to human health and so it can only be applied by a vet.

Chemotherapy drugs, injected into the sarcoid

This is a treatment which we occasionally use for the most stubborn sarcoids in particularly bad cases. These drugs can be very dangerous to handle.

Surgical excision

This is a treatment which has had some bad press in the past. Often beacuse it may have been used inappropriately on large, poorly defined sarcoids. In such cases it is difficult to excise the entire sarcoid and regrowth often occurs more aggressively. Excision of smaller, well localised lesions where there is a clear margin of normal tissue around the sarcoid is a useful treatment. Sometimes we take the majority of a sarcoid off surgically but treat the remnant with cryosurgery - this surgical technique is known as "debulking".

Laser excision

More recently excision of sarcoids using surgical lasers has become very popular.  The mass is excised with a good margin to ensure all the cancerous cells are removed.  The laser cauterises the tissue edges concurrently stopping any skin bleeding.  The surgical wound is left open to heal by granulation. Most horses are comfortable very soon after the surgery, and although it takes a few weeks to heal completely the cosmetic outcome is usually very good.

Injection with BCG vaccine

BCG vaccine is usually used for vaccinating people against TB. However it can be used to trigger the horse‚Äôs immune system into rejecting a sarcoid - Unfortunately this therapy is not currently available.

Implantation of radioactive wires

This has to be done at a university hospital with expertise in the procedure - Unfortunately this therapy is not currently available.


It is occasionally possible to successfully remove all of a horse's sarcoids but in many cases the treatment results in control rather than resolution of the lesions.