There are many different kinds of skin tumors. Some are serious but most are benign. Most skin growths are likely to be either skin papillomas (i.e. warts) or sebaceous gland adenomas. Skin papillomas are common in dogs. Their cause is unknown, although viral infections appear to be involved in some cases. These growths often appear as solitary or multiple lumps, and have a cauliflower-like surface appearance.
Warts can appear anywhere on the body, especially as dogs get older, but they cause few problems and are usually benign. In those cases where a wart causes a problem, such as when the dog licks it excessively or when the wart becomes infected, it can be removed surgically without difficulty. Usually, warts are left alone.
Sebaceous gland tumors derive from the sebaceous glands in the skin, which secrete an oily substance called sebum, which keeps the skin soft, pliable, and moisturized. These types of tumours are the most common kind of skin tumour in dogs, and are often confused with warts since they are similar in appearance. Like papillomas, sebaceous gland tumours are common in dogs. They usually appear on older dogs, and are more common on certain breeds such as Cocker Spaniels, Poodles, Boston Terriers, Kerry Blue Terriers, Beagles, Dachshunds, Norwegian Elkhounds and Basset Hounds. Sebaceous gland tumours are usually not surgically excised unless they cause problems.
As a rule of thumb, all growths should be checked out by your veterinarian to ensure that they are not malignant.