A small bulge behind a child’s ear may be caused by insect bite dermatitis, lymphadenitis, sebaceous cysts and other diseases. 1. Insect bite dermatitis: children’s ears behind a small bulge may be due to the presence of more mosquitoes in the living environment, when mosquitoes bite, the secretion of saliva and venom contains antigenic components. After entering the skin, then there will be a rash, itching and other symptoms. 2. Lymphadenitis: when a child is accompanied by otitis media and other diseases, it may lead to inflammatory reactions in the lymph nodes behind the ear. These patients may have small bulges behind the ear, pain on pressure, fever and so on. 3. Sebaceous cysts: Sebaceous cysts are retention cysts formed when the sebaceous gland ducts are blocked by various factors. When it occurs in the head and face area, it can be manifested as a small bulging bag, with no special discomfort in the early stage, smooth surface and clear boundary. There are more reasons for children to have a small bulge behind the ear, so seek medical attention if necessary to avoid further aggravation of the condition.