Sarcoids in Horses

What sarcoids are, how they can look, and why any new skin lump should be checked by your vet.

Quick Answer

Sarcoids are skin tumours and the most common skin tumour of the horse; they are locally invasive but do not spread to internal organs.
They can look like warts, flat scaly patches, firm lumps or fleshy ulcerated masses, so only a vet can say what a lump really is.
Ask your vet to examine any new or changing skin lump early, because early treatment generally gives the best chance of a good outcome.
Do not treat, pick at or rub a suspected sarcoid yourself, because inappropriate treatment can make it more aggressive.
Treatment is your vet's decision, and recurrence is common, so regular monitoring matters.

Sarcoids in horses are skin tumours that arise from fibroblast cells in the skin and connective tissue. They are the most common skin tumour of the horse. Horses, ponies, donkeys and mules can all be affected.

Sarcoids are locally invasive, which means they damage the tissue around them. However, they do not spread to internal organs. Some UK sources call them a form of skin cancer, so they should always be taken seriously.

Vets have many treatment options, although none works every time. This guide explains the types, the signs, and why your vet needs to be involved from the start.

What Causes Sarcoids in Horses?

A virus and a susceptible horse

Sarcoids are linked to bovine papillomavirus (BPV). The Royal Veterinary College describes it as the cause in genetically susceptible horses. Other UK sources are more cautious and say the cause is still debated.

Not every horse exposed to the virus develops sarcoids. Horses that are genetically susceptible are likely to keep developing them.

Does it spread between horses?

This is not fully understood. The Royal Veterinary College says spread by direct contact or by flies is unproven, and there is no evidence that horses with sarcoids are a threat to others.

Some other UK sources suggest that insects may be involved, but this is not proven. One equine practice adds that it is still not clear how transmissible sarcoids are, so it is common sense to take care with fly control, especially when a horse with a wound shares grazing with a horse that has sarcoids.

Age

Sarcoids can appear at any age. Young to middle-aged horses are most commonly affected.

Wound sites

Sarcoids may also develop at the site of a wound, where they can be mistaken for proud flesh. If a wound is not healing as expected, particularly on a limb, ask your vet to consider sarcoid change. Our guide to Horse Wounds: First Aid and When to Call the Vet covers the first steps for any wound.

The Six Types of Sarcoid and How They Can Look

Sarcoids are recognised in six types, although the names vary between vets. One horse can have several types at once, and a single sarcoid can mix features. Identifying the type matters, because the types differ in how aggressive they are and how they are treated.

Occult

Occult sarcoids are roughly circular, hairless or scaly patches. They can be subtle. Because of this, they are easily mistaken for ringworm or for rub marks from tack.

Verrucose (warty)

Verrucose sarcoids look dry, greyish, scaly and hairless, a bit like a cauliflower or a wart.

Chestnut pony with a long pale mane and pink halter grazing on grass – sarcoids in horses can appear on the head, chest, groin or almost anywhere on the skin

Nodular

Nodular sarcoids are firm, round lumps that are often smooth. They are common around the eyelids, armpit and groin, and they may become ulcerated.

Fibroblastic

Fibroblastic sarcoids are fleshy and quick-growing. They bleed easily and often have an ulcerated surface, so they resemble proud flesh. They can develop at wound sites or from other types.

Mixed

Mixed sarcoids show features of two or more of the types above.

Malignant (malevolent)

This type is rare and the most aggressive. It is fast-growing, often ulcerated, and can spread over a wide area. Some cases may have no treatment options. Thankfully, it is very uncommon.

Where Sarcoids in Horses Appear and What to Look For

Sarcoids can develop anywhere on the skin. Common sites include the head and face (especially around the eyes, ears and mouth), chest, armpit, groin, sheath, inner thigh and abdomen.

A new lump, wart-like growth or crusty, hairless patch that does not go away.
A lump that grows, ulcerates or bleeds if rubbed or knocked.
A sore that attracts flies in summer or becomes infected.
A wound that is not healing as expected, particularly on a limb.
Several lumps, because a horse with one sarcoid is likely to develop more.

Early lesions can look harmless, and they are sometimes missed completely under the coat. Regular, hands-on checks of your horse's skin are therefore worthwhile.

One general pattern from the Royal Veterinary College is that non-painful, non-itchy lumps are often sarcoids, painful lumps are often infection, and itchy lumps are often allergies. This is not a way to diagnose a lump at home. For other causes of lumps, see Why Does My Horse Have Hives or Raised Lumps?

When to Contact Your Vet

Any new or changing skin lump, whether or not it looks minor.
A lump that is growing quickly, bleeding or ulcerating.
A lump near the eye.
A wound that will not heal as expected, especially on a limb.
Any wound on a horse that already has a sarcoid elsewhere.

Ask your vet promptly rather than waiting to see what happens. Early treatment generally gives the best chance of a good outcome, and well-developed sarcoids are far harder to treat.

What Not to Do With a Suspected Sarcoid

Do not try home treatments of any kind. Vets do not recommend this route, and each sarcoid needs assessing before any treatment starts.
Do not pick at, rub or interfere with the lump. Trauma of any nature is likely to aggravate it.
Do not use homeopathic or herbal preparations, as their safety and effectiveness are unproven.
Do not assume a lump is "just a wart". Sarcoids can look like warts but are not warts.

Inappropriate treatment can convert a simple sarcoid into a much more aggressive one, very quickly. Rubbing by tack can also make a sarcoid worse, so speak to your vet about any lump that tack may touch.

How Vets Diagnose Sarcoids in Horses

Diagnosis is often made by a visual examination of the typical features and sites. Some UK vets do not routinely advise a biopsy, because sarcoids can deteriorate after they are interfered with. A biopsy is therefore a decision for your vet.

If a biopsy is done, treatment should follow promptly. Your vet will also check the type, size, number and position of the lumps.

Treatment and Outlook

There is no universal best treatment and no "magic cure". Your vet will choose based on the type, size, number and location of the sarcoids, plus the horse's temperament and cost. A combination of approaches is often considered most effective.

What vets may do

For a small new lesion, your vet may advise monitoring only. Other UK options include laser or surgical removal, treatments applied directly by the vet, immunotherapy for lesions around the eye, banding, freezing (cryotherapy), radiotherapy and electrochemotherapy.

Some treatments involve hazardous substances, so they must be applied by a vet. Radiotherapy is available only at specialist centres.

What to expect afterwards

Treated sarcoids can look worse before they improve. They may swell, turn black or become inflamed. Treatment must also continue until there is a good response, because stopping early risks a worse recurrence.

The longer-term picture

Sarcoids do not usually self-cure, although some stay small for years. Recurrence is common after any treatment, so a treated horse needs regular monitoring for progression.

Horses do not die of sarcoids as such. However, some are put down because the sarcoids stop them working or enjoying a good quality of life.

Prevention, Buying a Horse and Medicine Records

There is no way to prevent sarcoids and no vaccine is currently available. Some UK equine practices suggest good fly control in summer and covering any wounds as sensible precautions, but how sarcoids spread is not fully understood, so these steps are not a guarantee. Any wound on a horse that has a sarcoid elsewhere should get veterinary input as soon as possible.

If you are buying a horse, look at any skin lump carefully, even if the seller says it is "just a wart", and ask your vet. Insurers usually exclude treatment for sarcoids that were already present when the horse was bought.

Horses must have a passport, and whether it declares the horse as intended for human consumption decides which medicines can be used. If you compete, document every treatment and its dates, and talk to your vet about detection and withdrawal times before you compete.

How Pet Med Direct Can Help

A suspected sarcoid needs a vet's examination, so please start there. Please do not order or apply anything to a lump before your vet has seen it.

If your vet prescribes a medicine for your horse, you can read how pet prescriptions work with us. You can also browse our equine range.

Some pet medicines require a valid veterinary prescription. Pet Med Direct can only supply prescription medicines after the prescription has been checked. Always follow your vet's advice and the directions on the medicine label.

Frequently Asked Questions

Are sarcoids cancerous?

Sarcoids are skin tumours. They are locally invasive but do not spread to internal organs. Some UK sources call them a form of skin cancer, so they should not be dismissed as harmless.

Can sarcoids spread to other horses?

The Royal Veterinary College says there is no evidence that horses with sarcoids are a threat to others. It is still not clear how transmissible they are, so ask your vet about sensible precautions. Some UK sources suggest insects may be involved, but this is not proven.

Is it a wart or a sarcoid?

Sarcoids can look like warts, but they are locally destructive and are not warts. Occult sarcoids can also be mistaken for ringworm or tack rub marks. Only your vet can tell them apart.

Can I put something on a sarcoid myself?

No. Vets do not recommend home treatments, and interference can make a sarcoid more aggressive. Ask your vet to assess the lump before any treatment starts.

Will a sarcoid go away on its own?

Sarcoids do not usually self-cure. Some stay small for years, but they still need monitoring. Ask your vet to check any lump and to advise whether it should be watched or treated.

Can a horse with a sarcoid still be ridden?

It depends on the lump. Small, flat sarcoids may not interfere with ridden work, but sarcoids under tack are a problem. Your vet can advise for your horse.

Can sarcoids in horses be prevented?

There is no way to prevent them and no vaccine is currently available. Regular skin checks help you spot new lumps early, so your vet can act sooner.

Do sarcoids come back after treatment?

Recurrence is common with any treatment. For this reason, treatment should continue until there is an effective response, and treated horses need regular monitoring.

Related Equine Health Guides

Sources and Further Reading

This article was researched from the sources listed above. It is general information for horse owners and is not a substitute for advice from your own vet.

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This article is for informational purposes only and does not constitute veterinary advice.
If you are concerned about your horse’s health, please consult a qualified veterinarian.