A lipoma is the most frequently observed non-malignant skin tumor in dogs, composed of mature fat cells. These benign masses of fat tissue accumulate just beneath the skin, most often in middle-aged to older dogs. Understanding the typical characteristics of a lipoma can provide initial context when a lump is discovered. Lipomas are generally slow-growing and do not spread to other parts of the body.
The Distinctive Appearance and Feel
The most defining characteristic of a simple lipoma is its texture, which is soft, doughy, or rubbery to the touch. Owners often describe the feel as similar to a small, soft rubber ball or a beanbag just under the skin. These fatty tumors are usually round or oval and can range significantly in size, from a small pea to a large orange.
A key physical trait is their mobility; a simple lipoma is often freely movable and not fixed to the underlying muscle or tissue. When gently pushed, the mass tends to slide easily beneath the skin. Lipomas are generally painless when touched, and the overlying skin usually appears normal without redness or ulceration. The size of the lipoma can fluctuate slightly if the dog loses weight, though the mass itself will not disappear completely.
Common Locations and Types
Lipomas can develop anywhere fat is present, but they are most commonly found on the trunk, including the chest, abdomen, and back. Other frequent locations include the upper legs and the armpit area (axilla). Dogs may develop a single lipoma or multiple growths across different areas of the body.
The majority are classified as simple lipomas, meaning they are encapsulated and easily separated from surrounding tissues. A less common type is the infiltrative lipoma, which is still benign but tends to grow into adjacent structures like muscle and connective tissue. This infiltrative type may feel less movable and firmer because it is interwoven with deeper tissues. Only a veterinarian can definitively distinguish between these two types, often requiring advanced imaging or a biopsy.
Differentiating Lipomas from Other Lumps
While the soft, movable nature of a lipoma is reassuring, not all lumps with a similar feel are benign. Other types of masses, including some malignant tumors, can sometimes present with a soft or rubbery texture. A lump that is growing rapidly, feels firm or hard, or is fixed and immovable to the underlying structures is more concerning.
Signs that a lump is likely not a simple lipoma include causing pain when touched, having an ulcerated or red surface, or feeling hot. These characteristics could indicate an abscess, a cyst, or a more aggressive tumor like a mast cell tumor or a soft tissue sarcoma. Because a small percentage of fatty tumors can be the malignant liposarcoma, any new lump should be evaluated by a veterinarian for an accurate diagnosis.
Diagnosis and Management Options
The standard procedure for diagnosing a lump is a Fine Needle Aspiration (FNA). During this minimally invasive test, a veterinarian inserts a small needle into the mass to collect a sample of cells for microscopic examination. If the sample consists primarily of fat droplets and mature fat cells, the mass is confirmed as a lipoma.
For small, non-bothersome lipomas, the most common management approach is watchful waiting, which involves monitoring the mass for changes in size, firmness, or appearance. Surgical removal may be recommended if the lipoma grows quickly, interferes with the dog’s movement (such as near a joint or in the armpit), or is an infiltrative type. Simple lipomas are easy to remove and rarely recur, while infiltrative types require more extensive surgery to ensure all invading tissue is excised.