People are alive, so the body has metabolism every day. This is because the cells of the human body are constantly active and renewed. As long as people are alive, excretion and sweating are normal body functions, even the ear holes are no exception. There are also foreign substances that are metabolized on the surface of the skin, because the ear studs directly block the ear holes, so the foreign matter accumulates on the ear studs, and it is mixed with sweat and moisture, dust, etc. in the air over time. The body also has body temperature, so that these foreign objects will produce odor.