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The essentials 

  • Hematomas and seromas are different — Hematomas (sometimes called blood blisters) are different from seromas, which are defined as clear fluid pockets in the skin.
  • Head shaking, injury, or surgery can cause hematomas — However, hematomas are also a common side effect of injuries and post-surgery healing in dogs.
  • Healing a hematoma usually requires the help of a veterinarian — Awareness, good hygiene, and regular pet care can help prevent them.

What is a hematoma and seroma in dogs?

A hematoma is a blood-filled sac or collection of blood under your dog’s skin. While this is one of the most common locations, hematomas can occur in many different areas of the body. Aural (ear flap or pinna) and scrotal hematomas (or hematomas located around your dog’s ear and groin area) are the most common.

A seroma is similar, except that the sac contains serum without any red blood cells.

Common symptoms of hematomas and seromas

The signs of hematomas in dogs depend on where the hematomas are located. The same can be said for seromas, which feature similar symptoms. Here are some common symptoms you might see with hematomas under the skin in dogs:

  • Swelling – Localized swelling can be normal if your dog is dealing with a hematoma or a seroma. 
  • Discoloration of the skin – Discoloration around the site of the hematoma or seroma is a common symptom of both conditions. Colors can range from red, to blue and purple. 
  • Deformity – This symptom is most commonly seen with ear hematomas and is also called cauliflower ear
  • Pain – Many dogs experience pain or touch aversion, as the hematoma or seroma area can be tender. This symptom can also be shown by scratching, head shaking, or whining. 
  • Hot skin – The location of the hematoma or seroma will usually be hot to the touch, possibly due to the blood flow in the area. 

Aural hematoma, from Noah’s Ark Pet Hospital of Amarillo

Hematoma under the skin, from Adobe Stock Photos

All hematomas generally look similar, no matter where they occur on your dog’s body. Learning to identify these can help you to get your dog the help they need quickly.

Causes of hematomas in dogs

Hematomas in dogs happen when blood vessels burst and cause blood-filled blisters. The blisters are painful and often form due to injury, scratching, ear infections, or other responses to irritation. See more below on the common causes of two of the main types of hematomas.

Most common types of hematomas and seromas in dogs

Aural hematoma

Hematomas and seromas of this type form near your dog’s ears. If your dog’s ear canal smells bad or has discharge, it is time to see your vet. In addition, keep your dog’s ears clean, dry, and well-groomed to prevent things like ear mites or bacterial or parasitic infections.

Scrotal hematoma

These types of seromas and hematomas are located near your dog’s nether regions. Neutering or spaying your dog at a young age (between 6-12 months) and restricting activity following the procedure will reduce the risk of your dog developing a hematoma. Follow all of your veterinarian’s post-surgical instructions including giving pain medications or anti-inflammatories, cold packs, or other specific practices.

Additionally, trauma-induced hematomas on other parts of a dog’s body can be avoided with proper care and a watchful eye to prevent accidents and injuries.

⚠️ Routine check-ups are your best option when it comes to early diagnosis and treatment. Not all hematomas or seromas can be felt by palpation alone and may need clinical review and imaging to confirm. This can be especially true for internal hematomas and seromas.

Diagnosing hematomas and seromas in dogs

Your vet has many different options when it comes to diagnosing hematomas and seromas in dogs. Often, they’ll palpate the area around the hematoma or seroma—feeling for fluid beneath the surface that could be causing the swelling. They may also draw fluid from the area, using microscopy to come to a final diagnosis. Hematomas and seromas can also be diagnosed via imaging tests (such as an X-ray, MRI, or ultrasound).

Treatment for hematomas and seromas

The treatment options for dogs with hematomas and seromas depend on the type of hematoma, the underlying cause of it, the location on the animal’s body, and the level of pain involved.

Natural healing

Some hematomas can heal on their own, but this can take several weeks and can leave your dog in pain and discomfort. There is a risk of forming new blisters if your dog further damages the affected area with scratching, chewing, or head shaking. There’s also a chance for permanent disfiguration and scar tissue. Your vet can help you determine if this is a viable course of treatment in your dog’s specific case. 


Depending on the size and location, your veterinarian may drain the hematoma of blood . However, simply using a needle to drain the sac has a high risk of recurrence and is not generally recommended.


Surgical intervention may be the next best treatment option for hematomas and seromas, especially with scrotal hematomas or internal hematomas that aren’t near the skin. With surgery, the blood is drained, the clotting is removed, and the area is sutured so that blood cannot re-enter. If it’s an aural hematoma, the ear(s) may be supported by a bandage or other material applied directly to the ear flap, or by bandaging the ear against your dog’s head. 

If you opt for surgery, know your pup will likely need to wear an Elizabethan collar to prevent scratching at small sutures on the surgical site. A follow-up check will also be needed to remove sutures and ensure there aren’t any additional blood clots forming.

While this can cause a slight permanent change to the skin due to the extra weight of the ear flap, it can get you good results—reducing blood-filled swelling of the skin and your dog’s discomfort overall. 

🚨 With most hematomas, some form of veterinary care is required for proper treatment.

Frequently asked questions

If it’s a blood blister, won’t it disappear with time, just like a bruise?

This depends on the type of hematoma. If left untreated, an aural hematoma may be slowly reabsorbed, but the associated inflammation will cause damage to the surrounding ear tissues resulting in a distorted, cauliflower-shaped ear. 

Other hematomas elsewhere on the body could be an indication of an active bleed and should be evaluated by your veterinarian to rule out anything more serious. The hematomas themselves also require treatment, as they can become infected without intervention. 

How do I prevent aural hematomas and seromas? 

Excessive scratching, head shaking, or “striking” of the ear can lead to hematomas and seromas in your pet. While you may not be able to prevent your dog from scratching both their external ears and internal ears, be sure to inform your veterinarian if you notice your dog itching more than normal. Your vet can test your dog for allergies, skin issues, or ear issues before a hematoma develops. 

Can you just drain the swelling?

Drainage may result in a temporary correction, but in the vast majority of cases, the hematoma returns within one to two days. The longer the hematoma is left untreated the greater the likelihood of permanent damage and disfigurement. Drainage may be used if the hematoma is very small, or if the dog cannot undergo surgery for some reason.

Can hematomas develop internally, too?

While most develop under the skin, it’s possible to have a hematoma develop internally. Symptoms of internal hematomas depend on which organ(s) are involved. For example, hematomas of the lungs may cause bloody spit, coughing, and difficulty breathing while hematomas of the spleen may cause swelling of the abdomen or collapse. Other serious symptoms include seizures, comas, neurological damage, pain, and incontinence. These types of hematomas are very serious and require immediate medical attention.