The skin of the cartilaginous part of the normal external auditory canal has sebaceous glands, almost all of which have ducts opening into the lumen of the hair follicle. This secretion is extremely small and usually does not constitute an overflow. When inflammation, metaplasia or tumors occur in the external auditory canal, a plasma, plasma blood or purulent secretion can occur. So, what should be the differential diagnosis of what causes ear overflow? The following is a detailed description: 1. External ear canal boils with limited redness and swelling of the external ear canal, severe pain and obvious pressure pain of the ear screen and pulling pain of the ear wheel. After the abscess breaks down, pure purulent secretion, small amount and numerous fluids flow out. 2. External ear eczema with diffuse or limited superficial skin erosion and oozing in the auricle, ear canal, and postauricular groove. The exudate is a yellowish plasma exudate with varying amounts. After evaporation, a yellowish-brown scab is formed. 3. Diffuse otitis externa with superficial erosion of the skin of the external ear. The early stage of acute infection is a thin plasmacytic discharge, which gradually becomes a thick purulent discharge. The tympanic membrane is intact. 4. Mycosis of the external auditory canal, which is susceptible to development in humid environments. Deep in the external auditory canal, even the surface of the tympanic membrane covered with yellow-brown membranous material, dry state can be powdered, moist as a moist ink-absorbing paper-like film, with strange itching. When the membrane is removed, the surface of the tympanic membrane is vesiculated, congested, and exuded with plasma.