The odor behind the ear may be caused by physiological factors, bacterial infection, sebaceous cysts and other factors. 1. Physiological factors: when the back of the ear is not cleaned for a long time, there is dirt in the area of the groove behind the ear, and there is a lot of dirt, so when you touch it with your hand, you will feel a bad smell, but there are no other clinical symptoms, and the smell will disappear after it is cleaned. 2. Bacterial infection: when there is bacterial infection in the skin behind the ear, the bacterial metabolites mixed with sweat will have a foul odor. 3. Sebaceous cysts: Sebaceous gland secretion and poor hygiene may lead to sebaceous cysts, not timely cleaning, there may be purulent substances generated, there will be a bad smell, after the cysts increase, there will be obvious pain. If the odor behind the ear is not relieved after washing, it is recommended to consult a doctor for a clear diagnosis.