Health Topics  >  Skin and Coat  > Lumps and Masses

What causes skin lumps and bumps in dogs?


Dogs experiencing an allergic reaction may develop small bumps on their skin called hives, just like humans with allergic reactions. In this case, their fur will feel bumpy when you pet them, and the hair may look raised in some areas. This reaction can occur pretty quickly following contact with an allergen (ex. certain plants, insects or foods), and if you notice them it is important to ensure that your dog is not having any breathing difficulties as more severe allergic reactions can cause swelling within the mouth.

Contact your veterinarian if you have any concern regarding their breathing or if your dog becomes very itchy. 

Dogs can develop hives on their skin from allergic reactions. Look out for more severe symptoms of allergies, like breathing difficulties or facial swelling.


Abscesses are generally soft, squishy swellings under the skin due to an accumulation of pus (they often feel like a large fluid filled blister). Abscesses occur when bacteria gets under the skin, usually from something like a stick poking through the skin or an animal fight, allowing bacteria to enter. The puncture site may not be visible, and sometimes  pus may be draining from the abscess at the time it is discovered. If enough pressure builds up under the skin as the abscess gets larger, these swellings will rupture and the contents will begin to drain out.

Typically, your veterinarian will flush the abscess to remove the pus and start your dog on a course of antibiotics. 

Example of an anal gland abscess. This accumulation of pus will likely get larger and is at risk of infection.


Sebaceous cysts are small hairless wart-like masses that grow from the skin and sometimes release its contents onto the skin. They’re affectionately known as  ‘old dog warts’, although they can appear at any age. Some cysts remain present for years while others disappear on their own. These cysts are usually benign but can be irritating or become infected.

Many owners choose to have cysts surgically removed due to their appearance or if they become ulcerated due to scratching. Breeds such as Poodles and Bichon Frises are prone to sebaceous cysts.


Lipomas are usually moderately soft, round masses made up of fat cells located under normal looking skin. They are usually moveable and slow growing. Lipomas are composed of benign fat cells, and can be removed for cosmetic reasons or can be left alone if they are not bothering the dog. In more rare instances, lipomas can be malignant and therefore are a cause for concern (known as a liposarcoma).

If your dog develops a new mass that is suspected to be a lipoma, your veterinarian will likely discuss doing a test called a fine needle aspirate to confirm whether the cells are benign. Breeds such as Labradors and Miniature Schnauzers are prone to lipomas.

Swollen Lymph Node(s)

A firm swelling in distinct locations under your dog’s skin, may be an enlarged and swollen lymph node. The easiest to palpate lymph nodes, meaning those you can feel through a dog’s skin, are located under their jaw, in front of their shoulders, and behind their knees. Like in humans, an enlarged lymph node most commonly indicates infection in a part of the body in which the tissue drains through that lymph node.

In rarer cases, an enlarged lymph node could be indicative of lymphoma. If there is no clear reason as to why lymph nodes are enlarged, your veterinarian will likely suggest further testing to identify the cause.

dog lymph nodes jaw shoulders armpits knees
The most visibly obvious and palpable lymph nodes in a dog are located under their jaw, in front of their shoulders, in the armpits and behind their knees.

Tumors – Benign or Malignant

Tumors can either be benign, in which case there is no concern for spread, or malignant, meaning there is a risk of the tumor spreading to other organs in the body. It is not possible to definitively differentiate the two types without sampling them, which involves sticking a needle into the lump to collect cells to look at under a microscope (known as a fine needle aspirate or FNA) or removing at least part of the mass for examination of cells under the microscope.

Your veterinarian will discuss with you what is the best option for your pet with the highest chance of yielding a definitive answer.

A common, inexpensive and minimally invasive diagnostic procedure for lumps is the Fine Needle Aspirate (FNA), which involves taking a sample of cells and observing it under a microscope.