What is the Difference Between Sarcoids and Melanomas in Horses?

Skin lumps are a common concern for horse owners, and two of the most frequently diagnosed skin tumours in horses are sarcoids and melanomas.

Although they can sometimes look similar at first glance, they are very different in origin, behaviour, and management.

Understanding the difference can help you know when to monitor, when to call your vet, and what treatment options may be available.

What Are Sarcoids?

Sarcoids are the most common skin tumour seen in horses. They are locally aggressive skin growths that do not spread to internal organs, but they can grow, recur, and become problematic if irritated.

Sarcoids are associated with the Bovine papillomavirus, which is thought to play a role in their development.

What Do Sarcoids Look Like?

Sarcoids can vary widely in appearance. They may appear as:

• Small, flat, hairless areas
• Wart-like growths
• Crusty or scabby lesions
• Firm nodules under the skin
• Large, ulcerated, fleshy masses

They are commonly found on:

• Around the eyes
• Ears
• Groin
• Armpits
• Chest and sheath area

Key Features of Sarcoids:

• Can occur in horses of any colour or breed
• Often develop in younger horses (but can occur at any age)
• May grow slowly or rapidly
• Can worsen if traumatised or improperly treated
• Do not spread internally, but can be locally invasive

Because sarcoids can become more aggressive if interfered with, early veterinary assessment is always recommended before attempting any treatment.

What Are Melanomas?

Melanomas are tumours that arise from pigment-producing cells (melanocytes). They are particularly common in grey horses.

Unlike sarcoids, melanomas are associated with coat colour genetics rather than a virus.

What Do Melanomas Look Like?

Melanomas typically appear as:

Firm, round nodules under the skin
Black or dark grey masses
Smooth and well-defined lumps

They are most commonly found:

Under the tail
Around the anus
On the lips
In the parotid (cheek) area – back of the jaw
Around or inside the sheath in males

Key Features of Melanomas:

Very common in grey horses, especially over 6–8 years old
Often slow-growing initially
Can become larger and more numerous over time
In some cases, may spread internally in later stages

While many melanomas remain benign for years, some can become malignant and cause complications depending on size and location.

When Should You Call Your Vet?

You should seek veterinary advice if:

A lump changes in size, shape, or appearance
It becomes ulcerated, bleeding, or painful
It interferes with tack or movement
Your horse is a grey developing new lumps under the tail
You are unsure what the lump is

Importantly, not all lumps should be biopsied immediately, particularly suspected sarcoids, as interference can sometimes stimulate growth. A proper clinical assessment allows us to recommend the safest approach.

Treatment Options

Treatment depends on:

Location
Size
Type of tumour
Your horse’s age and use

Options may include:

Topical therapies
Surgical removal
Laser surgery
Immunotherapy
Monitoring in stable cases

Every case is different, and early intervention often provides the best outcome.

So…

While both sarcoids and melanomas are common in horses, they are very different conditions with different causes, behaviours, and treatment approaches. Early diagnosis and a tailored management plan are key to preventing complications.

If you notice a new lump on your horse, don’t ignore it - and don’t attempt home remedies before speaking to your vet.

At North West Equine Vets, we’re always happy to assess skin lumps and advise on the best course of action for your horse. If you’re concerned about a sarcoid or melanoma, get in touch 0808 168 5580 we are always happy to advise.