Otitis externa can be divided into two categories, one is localized otitis externa, also known as external auditory canal furuncle. The other is diffuse inflammation of the external auditory canal skin, also known as diffuse otitis externa. Diffuse otitis externa is caused by gram-negative bacteria, such as Escherichia coli, Pseudomonas aeruginosa or Proteus vulgaris, Staphylococcus aureus, or few fungi. Furuncle of external auditory canal is often caused by Staphylococcus aureus. Some people (such as allergic reaction, psoriasis, eczema or seborrheic dermatitis) are particularly prone to otitis externa. External auditory canal infection can be localized (furuncle) or involve the whole external auditory canal (diffuse otitis externa). Inducing factors include: ear damage caused by water or various irritants, such as hair gel or hair dye, entering the external auditory canal and wiping the ear canal. Through desquamation of epithelium, desquamation moves outward from the outside of tympanic membrane like a conveyor belt, and cleans the external auditory canal by itself. The patient manually cleans the external auditory canal (wipes the ear) with a cotton swab, which interferes with the self-cleaning mechanism. Because the direction of ear rubbing is opposite to the direction of epithelial desquamation, it can push debris into the ear canal and promote desquamation aggregation. Debris removal and earwax absorb water entering the external auditory canal, which softens the skin and creates conditions for the invasion of pathogenic bacteria.