Acne behind the ears is mainly caused by inadequate cleansing, as the sebaceous glands become clogged due to the constant accumulation of sebaceous secretions. Sebaceous glands become clogged and secretions from the sebaceous glands are not discharged in a timely manner, gradually accumulating to form a cystic-like swelling. When squeezed, a pea-like secretion may appear, sometimes with a foul odor, and is often found on the head, face, neck, chest and back. If you have a powdery tumor behind your ear, you must bathe frequently to prevent or control the growth of the tumor. If the size of the pimple is small without any symptoms, it can be temporarily observed. If there is repeated infection, pus or the size increases significantly, it can be treated through surgery.