Finding a lump on your pet’s skin can be worrisome. How do you know if it is something bad? What should you do about it? There is a very long list of things that cause lumps on skin. Some of them are innocuous some are very serious. Here are some of the more common types of benign lumps that I see on pets, and the ways we identify and treat them. Next time we will talk about some of the more common problematic lumps.
Sebaceous cysts: The sebaceous glands are skin glands that excrete a waxy substance called sebum on to the surface of the skin. Sebum keeps the skin soft and haircoat shiny. Sometimes the openings to a sebaceous gland get tucked under the surface of the skin and instead of secreting the sebum onto the surface of the skin the glands secrete sebum into a pocket underneath the skin that grows into a lump as the waxy material accumulates with nowhere to go. These are known as sebaceous cysts and they are completely non-cancerous. Although the sebum can sometimes be squeezed from the pocket like popping a zit, the cyst will usually continue to return unless the section of abnormal skin that is producing the pocket is surgically removed. Because the vast majority of sebaceous cysts sit quietly and don’t cause any health problems the recommendation is usually to ignore them. If they are very large, become infected repeatedly (a common result from being poked frequently to drain the wax), or are otherwise making a nuisance of themselves they can be removed fairly easily. Some dogs will make one or two small cysts and some dogs have a tendency to make many. Cats occasionally develop sebaceous cysts too, but not as frequently as dogs. Cats and dogs can also develop cysts that are filled with a watery fluid. They can expand rapidly like a water balloon, but when pierced with a needle the liquid rapidly drains out of them. These cysts rarely cause a health threat, and their permanent cure also requires excision of the abnormal skin making the fluid pocket, or the lump will fill up again and again no matter how often it is drained.
Sebaceous Adenomas: Those sebaceous glands are back at it, but this time the cells lining the inside of the gland have proliferated excessively and have created a little cauliflower textured lump on the surface of the skin. I believe it is a legal requirement that all small, white dogs over the age of 6 years must have at least one sebaceous adenoma. By the age of twelve many dogs will have bumper crops of them sprouting all over their bodies. These lumps are commonly called warts, but they are not contagious like the viral warts that people tend to get on their hands. Once again, surgical removal is the only way to get rid of these lumps, but because they do not cause systemic problems I only recommend removal if certain lumps are causing irritation.
Histiocytomas: These are pink raised lumps that appear on the surface of the skin over the course of a few weeks or a few months. They are the most common type of skin tumor we see in dogs under five years of age. Boxers and Pit Bulls are particularly prone to developing them, but any breed could be affected. When these lumps are left alone the immune system eventually wakes up and realizes that they are not supposed to be there and it sends in the cavalry to fizzle the lump away from the inside out in a process that takes from about 2 weeks to one month. The lump often becomes ulcerated and scabby. When the scab comes off the lump is usually gone. The problem with histiocytomas is that to the naked eye they are indistinguishable from other more serious types of skin cancer. Your veterinarian can only uncover the identity of a lump by using a needle to collect some of the cells and then look at them under a microscope. If there is any doubt, surgical removal is completely curative.
There are hundreds of things that can cause lumps on the skin, and these are just a few of the common ones that are not health threats. Unless your veterinarian paid better attention during Psychic Powers 101 than I did, however, there is no way to make a determination about whether a lump is a problem or not without seeing the patient and doing some testing to determine what the lump is made from. At least you know that it isn’t always bad news when you find a lump, so don’t be afraid to find out the answer.