Finding lumps, bumps and swellings on the skin of horses is a very common problem for owners. In this article, veterinarian Dr Rachel Kent sorts the harmless lumps from the nasty bumps to help you identify ones that may  require veterinary treatment, versus those which may be left alone.

Where to start

Lumps, bumps and swellings can be temporary blemishes or a permanent disfigurement. They vary in appearance and size, and be anything from a slightly raised area, through to having a combination of erythema (reddening), alopecia (hair loss), crusting, scabbing, pruritis (itchiness), pain, sores, scaling or thickening of the skin.

Wherever the location of the lump or bump on the horse, all diagnosis of skin lumps and bumps starts with a history.

This will include:

  • Age, breed and sex, coat and/or skin colour.
  • How long has the lump has been there?
  • Has it increased or decreased in size?
  • Has something in particular happened, for example, a trauma?
  • Has it discharged and, if yes, what material came out?
  • Is it pruritic (itchy)?
  • Is it painful?
  • What has changed for the horse in terms of diet and environment?
  • Have you introduced other horses and, if yes, how long ago?
  • Has your horse been off the property, where to, and how long ago?
  • Has your horse been wormed and/or vaccinated?
  • How is their overall health in regard to appetite, drinking, urination and faeces output?
  • And importantly, response to treatment – what have you used to treat the problem and has it responded to treatment, stayed the same or got worse?

The answer to these questions can be of great assistance to working out the cause of the problem for your horse.

After this, your horse will require a general physical examination and, following this, a thorough examination of the skin lumps. Samples are commonly collected from lumps, and include a sticky tape preparation and a skin scraping, which enable staining and examination of the cells under a microscope, also known as cytology. Your veterinarian may also perform a fine needle aspirate, extracting some cells via a needle and examining those cells under a microscope.

Sometimes, in order to provide a definitive diagnosis, a biopsy of the lesion or lesions needs to be collected for histopathology examination, or a sample taken to grow a culture of any bacteria or fungi that may be present.

Occasionally, lumps and bumps, particularly those on limbs, need to be examined further using radiographs to check for bony involvement, or by ultrasound to examine the structure of the underlying soft tissue.

Inflammation and physical conditions

Trauma is one of the most common causes of lumps, bumps and swellings. Often, the new horse in the paddock has been kicked by another or the horse has hit an object – the fence or a tree being common culprits. Inflammation by pathological definition causes redness, heat, pain and swelling. Lumps from trauma are due to swelling between the cells of the tissues, along with pooling of blood and inflammatory fluid.

Alternatively, the trauma may cause a pocket to form that fills with either blood, called a haematoma; inflammatory fluid, known as a seroma; or when over a tendon or joint, synovial fluid is known as bursitis. These pockets of fluid, depending on their size, are often drained to enable the injury to heal faster and with less scar tissue.

Swelling caused by trauma will resolve in time. However, it may cause thickening and scarring of the skin or fibrosis, leaving a permanent blemish. The location of the swelling will determine if there is any impact on movement and hence, subsequent performance.

Acute injuries should be treated with cooling from ice packs or cold hosing, application of a topical anti-inflammatory product or poultice, and rest and compression bandaging, where possible.

Any skin injuries will need to be cleaned and treated. If the wound is deep or bleeding profusely, or you are at all worried, you should call your vet.

Muscle tears can cause protrusion of the muscle tissue outside of the normal sheath and will be associated with increased swelling from inflammation when they first occur. Muscle tears can also have an impact on the biomechanics of your horse (the way it moves).

After the initial swelling has resolved and if your horse is not showing any signs of lameness or pain, then it is unlikely the swelling/thickened tissue is going to cause any problems, apart from being a permanent visual blemish.

Hernias are ruptures through the tissue wall. They are more common in the scrotum, inguinal or umbilical regions. However, abdominal hernias also occur and cause protrusion of abdominal contents through the muscle wall under the skin. Surgery is often required to repair hernias.

Foreign bodies, such as grass seeds and sticks, are a common cause of swelling, and can be very challenging to locate and remove if retained in the body. Other times, they have gone in, but come out again, leaving a trail of bacteria in their path and causing inflammation of the damaged tissues.

The foreign body may cause formation of a draining tract, leading to a deeper underlying abscess that forms as the body attempts to ‘wall off’ the problem. The swollen area needs to be explored, and the foreign body and affected tissue removed for the injury to heal.

Infectious causes

Abscesses are a pocket of purulent material or pus containing bacteria, and normally occur secondary to trauma. They are treated by lancing to open them, followed by flushing and drainage. If not drained, they may put enough pressure on the overlying skin to finally burst and drain on their own.

Skin infections or dermatitis from bacterial or fungal infections also cause inflammation of the skin with localised swelling and often scabbing, crusting and raised hair lesions.

The two most common of these are rain scald and ringworm infection. However, secondary infections can also occur from self trauma when your horse is itchy, and many horses with chronic skin conditions will have thickening and folding of the skin that may resemble swelling.

Parasites are another reason for swellings or lumps, and commonly include the Habronema species and Onchocerciasis cervicalis.

Habronemiasis or Summer sores are caused by the stomach worm larvae that produce swelling and red/brown wounds that contain hard, calcified material, often around the eyes, genitalia or in open wounds. The lesions are open and sore, and can be difficult to treat.

Fly masks, deworming treatment with ivermectin or moxidectin, control of fly populations with manure removal and excision of excess inflammatory tissue is often required to manage this condition.

Onchocerciasis, or the pin neck worm, is transmitted by biting midgies. The larvae cause small nodules that form in the skin and can be very pruritic (itchy).

Eosionophilic granuloma nodules are distinct circular nodules in or under the skin between 5-10mm in size that can become calcified and are commonly found on the neck. They don’t normally cause a problem unless in an area where gear may rub, such as the girth or back, and require corticosteroids or surgical excision to treat them if needed.

Biting insects, flies, ticks and midges can all cause a 5-10mm diameter size slightly raised circular swelling on the skin that often have a small scab in the middle. These may or may not be itchy, however can enable secondary bacterial infections to occur if the horse is itchy.

Paralysis ticks, in particular, have been known to cause significant swelling with either a tick in the middle or a crater. Occasionally, the swelling can cause the sheath to swell or for there to be oedema or swelling under the belly or chest.

Changing paddocks or stabling during early morning and evening, rugging and using repellent insecticides will help prevent irritation from these insects. Most of these swellings and lumps will go away in their own with time. However they may need treatment if they cause a secondary bacterial infection.

Immune mediated

Hives, urticaria or wheals are raised irregular lumps and bumps that occur due to an allergic reaction. They appear rapidly in response to food, dust mites, pollens, certain plants or trees, and insect bites and can spread over the entire body. This condition is treated with antihistamines and corticosteroids systemically, and these lumps and bumps often disappear completely.

Neoplasia or tumors

Tumors, or neoplasia, are caused by abnormal growth of cells and can be benign or malignant.  There are numerous types of tumors. However, the most common of these are melanoma, squamous cell carcinoma, sarcoids and papillomas.

Melanomas are raised, dark pigmented or grey masses, seen often under the tail or in the neck and throat area. Anyone with an older grey horse can attest to these growths and over 90% of grey horses by the age of 9 will have them. They are normally slow growing and many horses can live with them or there are various treatments for them to be removed.

Squamous cell carcinomas are often a solitary lesion, raised, irregular and often become ulcerated. They can arise anywhere on the body, however are common in non-pigmented or poorly haired areas, and mucous membranes, such as around eyes, lips, nose, and on the sheath or vulva. They are malignant and treatment by your veterinarian is recommended.

Sarcoids. Anyone who has had a horse with a sarcoid will understand how challenging and frustrating these growths can be. There are now six classified types of sarcoid:

Occult sarcoid – these are roughly circular, flat and can be hairless or have alteration of the hair growth. Sometimes, the skin may be thickened slightly. They may look like a skin rub or ringworm (dermatophytosis) lesion.

Verrucous sarcoid – these are wart-like lesions and often have a grey or scaly appearance.

Nodular sarcoid – these are single or multiple lumps, or circular lumps that can be attached to the underlying skin or the underlying tissue.

Fibroblastic sarcoid – these are fleshy, raised growths that bleed easily and often look like granulation tissue.

Mixed sarcoid – these are combinations of the above lesions.

Malignant sarcoid – these are lesions that have spread into the skin and subcutaneous tissue, and are more extensively invasive. Fortunately, this is a rare form.

Sarcoids look like other skin lesions, such as a skin rub, wart or proud flesh, and other neoplasias.

To add insult to injury, sarcoids do not like to be interfered with and will often respond by increasing in size or spreading, making biopsy and removal of these growths a risk.

Hence, any growth suspected of being a sarcoid is better to be treated as a sarcoid, unless proven otherwise.

Treatment of a sarcoid is best advised by your veterinarian as there are multiple treatment options available, and location and size can determine the treatment plan. Image A shows nodular swelling on the flank region of this horse that are suspected to be nodular sarcoid growths.

Papillomas and warts

Warts or papillomas are common and there are two main forms caused by the equine papilloma virus (technically a papovavirus).

In young horses up to three years of age, they are benign and will resolve on their own with time. However, they are contagious to other horses.

Warts are often white to grey/black in colour, irregular shaped, raised growths that can be a single growth or in clumps.

How long they stay for can range from months to years. They are often a temporary blemish, but your veterinarian can remove them with surgery and/or liquid nitrogen, if required.

Congenital or genetic conditions

Often these disorders affect the integrity of the skin and are fortunately rare. Abnormal collagen and/or elastin causes loose, stretchy skin, such as occurs with Hereditary Equine Regional Dermal Asthenia (HERDA) or abnormal attachment between the inner and outer skin layers as with Epidermolysis bullosa syndrome. You may not see a lump or bump as such, however, the stretching of the skin may look like swelling.


There are many causes of lumps and bumps, and an even greater number of treatments available. However, when treating lumps and bumps, there are really only three options:

  1. Monitor it and see what it does.
  2. Treat it topically.
  3. Surgically remove it.

In some instances, owners are able to treat these conditions. However, if you are concerned, or if you have tried treating the lump or bump and it has not gone away or is getting worse, or if you suspect a sarcoid or neoplasia, then please consult your local equine veterinarian for diagnosis.

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This article appears in Horses and People May-June 2019 magazine