A skin mass or lump can be within the skin, in the tissues under the skin or attached to the skin and underlying tissues. Thus, any proliferation of cells, pocket of fluid or debris, or swelling of the dog's tissues can cause a mass. The health impact depends on the severity of the cause of the growth and the success in treatment of the problem.
The most common causes of skin growth are tumors, malignant and benign, bruises, infections and other causes.Malignant Tumors
Malignant tumors are proliferations of abnormal cancerous cells that endanger the dog by either invading nearby tissues or spreading to other areas of the body (metastasis). There are too many types of skin tumors to list here, but some of the more common ones are: Mast cell tumors. These are made up of great numbers of mast cells, a type of cell that is normally found within the skin. These cells normally release substances that are involved in allergic and immune responses. The massive amounts of these substances that can be released from tumors can be very dangerous to the animal. Tumors of this type can invade locally and metastasize.
Melanomas. These are tumors of the cell type that provides pigment to skin. They may be malignant or benign. Melanomas on the feet or in the mouth are likely to be very aggressive and dangerous. These tumors are usually black in color.
Fibrosarcomas. These tumors affect the cell type that helps to make up the connective tissue found under the skin. They rarely metastasize but are very destructive locally.
Squamous cell carcinomas are malignant tumors of skin cells that often occur at areas of unpigmented or lighter colored skin due to damage from the sun. They rarely metastasize but are destructive locally. They may also be non-solar induced.
Benign tumors are proliferations of cells that do not invade other tissues or spread to other locations. They are only dangerous when growing in a confined space, like in the head where they may compress the brain. They may need removal if they inhibit any important function or if they become damaged and bleed or become a nuisance. Some common benign tumors are listed below.
Lipomas are benign tumors of fat cells commonly found under the skin in dogs. These tumors are only a problem when they get very large or when they are in a location that interferes with the animal's movement.
Perianal adenomas are found under the tail in the skin next to the anus. They occur most commonly in males that have not been neutered. Your veterinarian will probably recommend neutering at the time the mass is removed to prevent future tumors. Fortunately, the malignant counterpart of this tumor, the perianal adenocarcinoma, is rare.
An abscess is a collection of inflammatory cells (white blood cells) that have been drawn to an area within or under the skin by the stimulation of an infectious agent (fungus or bacteria).
A hematoma is a blood filled space that can be found under the skin and is usually caused by trauma or by a defect in the clotting system.
Hives. When a dog has an allergic reaction, specific cells will release chemicals that cause swelling and redness in the skin.
A cyst is a space within or under the skin that is filled with fluid or cellular debris. Cysts are usually caused by abnormalities of skin glands.