Small bags behind baby’s ears may be caused by sebaceous cysts, boils, lymphadenitis, and insect bite dermatitis. 1. Sebaceous cysts: Sebaceous cysts are considered to be caused by the blockage of the sebaceous gland opening of the hair follicle and the accumulation of local sebum. Patients may present with round, medium hard cysts, so babies may present with the physical signs of a pouch growing behind the ear. 2. Boils: Boils may be caused by pathogen infections such as Staphylococcus aureus and Streptococcus. If boils appear behind the ears of babies, there will be localized red hemispherical nodules, pain and other manifestations, because babies will show signs of small bags behind the ears. 3. Lymphadenitis: Lymphadenitis may be caused by pathogens such as Staphylococcus aureus, hemolytic streptococcus and other infections. If the baby has lymphadenitis behind the ear, the local lymph nodes will be enlarged, red, swollen, painful and other symptoms, so the patient will appear as a small bag behind the ear. 4. Other: insect bite dermatitis and lipoma behind baby’s ear will also appear behind the ear with a small bag. It is recommended that babies need to consult a doctor in time if there are small bags behind the ears, and the doctor will choose the appropriate method of treatment after clarifying the cause of the disease.