There are several general causes. Insect bites: most commonly bees; allergies: vaccines, pollen, other items, etc.; trauma: whether he has been beaten, if he has been hit, etc.; effects of local tissues and organs: inflammation and swelling of lymph nodes, swelling of salivary glands, etc. In either case, the pet will need to be taken to the vet for consultation. Specifically, according to the clinician, the disease will need to be interviewed and the lesion area examined in order to have a preliminary judgement before appropriate treatment can begin.
