The exact cause of skin tags is up for debate. Some veterinary experts believe that skin tags and other skin tumors could be caused by exposure to the environment, like solar radiation. Others believe they’re caused by skin cell layers being exposed and constantly rubbed together, given that they tend to form around parts of the legs, neck, and other parts of the body that get a lot of friction. Another theory is that skin tags are potentially caused by a genetic predisposition, like many other skin disorders.