New Bump or Lump on a Cat’s Back or Tail: What is it?

“Doc, I found a new lump on my cat’s back when I was petting her…should I be worried?”

Sometimes in practice, I would receive a call or visit from a concerned client asking about a new bump. I would explain that the major reasons for bumps in the area of the tail and back include trauma, parasites, allergic reactions, abscesses, and tumors.

In this article, we’ll discuss major reasons for lumps on your cat’s back or tail, how to recognize them, and what you should do about them. We’ll explain what indicators tell you it’s time to go to the vet and how he’ll diagnose and treat your cat.

Five bumps or lumps that are often found on a cat’s back or tail

Lumps or bumps you may find on your cat’s back or around the tail usually fall into one of five categories.

1. Traumatic bumps

When your kitty injures herself, she may get a firm lump or a bruise. She can also develop a bump from an injection. Usually, traumatic bumps resolve on their own in a few days to a week. However, a cool compress may reduce swelling. If they persist, contact your vet because they can become infected. Pictured below is a lump on a cat’s tail as a result of trauma or injury. 

lump on a cat's tail due to injury

2. Parasites/Insects

Common pests and parasites may cause lumps and bumps to appear on your kitty. Certain spiders, mosquitoes, bees, and ticks are among the normal culprits. Although you may see a more pronounced reaction on the head or ears, bumps and welts can form along the back and tail. The bumps are frequently raised, red, and itchy. Learn more about common cat parasites.

lump on a cat's back from parasites

You may also find an embedded tick that feels like a skin tag.

lump is a tick that looks like a skin tag

One of the most common causes of lumps on a cat’s back or near the tail include miliary dermatitis and flea allergy dermatitis. This is the result of an allergic reaction to the saliva injected into the cat during a bite. Just one flea is enough to trigger flea allergy dermatitis. Most commonly, these scabs or bumps (small, firm, scabs) are found on the neck and on the back towards the tail (pictured below is a severe case):

Flea allergy dermatitis in cats

Treatment includes diligent flea control and corticosteroids for severely affected cats to reduce itching. Learn more about common cat parasites.

3. Allergic reactions

In addition to mosquitoes and other insects, some environmental irritants can trigger allergic reactions in cats. Hives usually develop and look like flattened or raised, itchy bumps.  Below is a picture that shows a rash and bumps on a Canadian Sphynx cat:

rash and bumps on a Canadian Sphynx cat

When your cat has an allergic reaction to something, she should see a veterinarian. If she shows signs of respiratory distress, head to the emergency clinic. Allergic reactions in cats are usually treated with antihistamines. Learn more about cat allergies.

5. Abscesses

Abscesses may develop on your cat from scratch, bite, or injection site injuries. They’re localized, walled-off infections. The pus pockets swell to form lumps that often become painful and warm to the touch. Cats with abscesses may also act tired and have a loss of appetite. 

Close up of abscess injury on a tabby cats leg

At home, you can apply a warm compress to help ease discomfort and swelling, but abscesses should be examined by a veterinarian. Your vet may drain the lump (as pictured below) and treat your cat with anti-inflammatory medications, pain relievers, and an antibiotic. If it’s a deep abscess, the doctor may surgically remove it. Learn more about cat abscesses and what to do.

draining abscess on a cat

6. Tumors

Only a few types of tumors may be found along the back or tail. 

  • Lipoma – A lipoma is a benign fatty tumor that often forms on the neck, flanks, or abdomen of older cats. Usually appearing in overweight felines, the tumors grow slowly under the skin. Lipomas don’t need to be removed unless they interfere with your kitty’s movement. Learn more about cat lipomas. Below is a picture of a lipoma on a cat’s back:


  • Fibrosarcoma – Sometimes caused by an injection, fibrosarcomas are rapidly growing cancers that may appear anywhere in the body. The masses start as small, firm lumps but grow quickly into the surrounding tissue. Click here to view a picture of fibrosarcoma on a cat’s back. Although they usually don’t metastasize to other organs, fibrosarcomas should be surgically removed to prevent further local damage. Follow-up treatment usually includes radiation or chemotherapy. The prognosis after surgery is guarded, and it varies depending on how aggressively the cells are dividing. Learn more about fibrosarcoma in cats.

If your cat’s bump or lump on their tail looks nothing like the images above, we invite you to read our page showing more lumps and bumps on cats, or keep reading this article to find out what you should do if you see a new bump on your cat’s back or tail.

What should you do if you see a new bump on your cat’s back or tail?

If you find a new lump or bump on your kitty, contact your veterinarian and describe the size, location, and consistency of the lump. Your doctor may recommend that you observe it for a few days to see if it resolves without further treatment. If it persists for more than a week, schedule an appointment.

How can I tell the difference between a cancerous and benign lump/bump?

Some distinctions between benign and cancerous lumps in cats are in the table below.

Characteristic Benign tumor Cancerous tumor
Growth rate Slow growth Rapid growth
Invasiveness Doesn’t invade local tissue Invades surrounding tissues
movement Moves under the skin when palpated Won’t move when palpated
shape Smooth and regular Irregular edges and shape

These characteristics may help you evaluate a new lump or bump on your cat, but the only definitive way to identify cancer is by conducting diagnostic tests. 

When should I call my veterinarian for a new lump?

If a lump suddenly appears on your cat, but she isn’t in distress or acting uncomfortable, you may attempt some at-home care for a few days. However, if the lump doesn’t disappear in a week or less, you should contact your veterinarian. Other reasons to call the doctor include:

  • Your cat is uncomfortable 
  • The lump is growing rapidly
  • The bump changes color
  • Your cat is having difficulty breathing
  • The lump has characteristics of a cancerous tumor

What should I expect when I take my cat to the vet?

When you take your cat in for an examination, be prepared to describe when you noticed the lump and whether it has changed in size or color. Also, share any symptoms such as tiredness or loss of appetite.

Once your vet examines your kitty he will assess the lump’s color, size, consistency, and movement. After that, your doctor will use diagnostic testing to determine the nature of the mass. Tests may include:

  • Fine needle aspirate for microscopic examination
  • Ultrasound or x-ray of the lump
  • Skin scraping/impression smear
  • Biopsy or complete surgical removal of the lump and pathologic examination

Depending on the diagnosis, your veterinarian will prescribe appropriate treatment.

  • Supportive care and anti-inflammatory medication to treat trauma
  • Antibiotics for abscesses and possibly as a preventative measure following trauma
  • Parasiticides to treat active parasite infestations followed by anthelmintic preventatives
  • Antihistamines or corticosteroids for allergic reactions
  • Surgical removal of tumors and possible radiation or chemotherapy

Cost of treatment ranges widely depending on the nature of the lump. If your kitty has a traumatic injury, the office visit and supportive care may run about $100-150. In the case of a cancerous tumor, the cost of surgical removal and follow-up therapy can reach $400-4,000 or more.

What lumps or bumps are more likely to appear on a cat’s back?

While there are several types of lumps that may appear on your cat’s back, the most common types you may see include:

  • Lumps caused by a traumatic injury
  • Lumps from parasites including embedded ticks
  • Abscesses from injections, bites, or scratches
  • Allergic reactions from insect/spider bites or an environmental allergen
  • Fibrosarcomas induced by an injection reaction – these lesions may be between the shoulder blades

What lumps or bumps are more likely to appear near your cat’s tail?

Many of the lumps that can appear on your cat’s back can also develop on or near the tail. However, the most common are:

  • Traumatic lumps
  • Abscesses 
  • Fibrosarcomas from injections if your veterinarian administers vaccines or medications in the hindquarters

Learn more about bumps and lumps on cats:

Lumps and Bumps on Cats [With Pictures]



  • Dr. Liz Guise, Veterinarian

    Dr. Elizabeth Guise (DVM) graduated from the University of Minnesota with a Doctorate in Veterinary Medicine. She worked as a veterinarian in private practice for over two years before going to work with the USDA as a veterinary medical officer for 14 years.