Uh-oh. What’s this lump? Any growth on your dog’s body deserves attention, especially one that wasn’t there last time you checked. It could be a sebaceous cyst (a sac filled with sebum, a cheesy or oily material, caused by clogged oil glands in the skin), an abscess (a pus-filled swelling caused by infection), or – everyone’s worst nightmare – a cancerous tumor. But in most cases, the lumps we discover as we pet and groom our dogs are lipomas, which are benign (non-cancerous) fat deposits, also known as fatty tumors. An estimated 1.7 million dogs are treated in the United States for lipomas every year, and according to one survey, American veterinarians average 25 lipoma removals annually at a cost to owners of $635 million. Lipomas tend to emerge as dogs reach middle age and increase in number as dogs get older. A dog with one lipoma is likely to get more. Lipomas are most often found on the chest, abdomen, legs, or armpits (axillae). These fatty lumps aren’t painful and they usually stay in one place without invading surrounding tissue.