Belly button inside the dirty things, may be formed by the following kinds of substances: the first, the belly button inside the skin after the stratum corneum, gathered in the belly button inside; the second, may also be the usual clothing worn clothing fibers or clothing of hair, cotton shreds in the skin stratum corneum mixed and formed; the third, should be the belly button inside the bacteria, the most common is gram-negative bacteria or Anaerobic bacteria, combined with the inside of the hair and cuticle in the inside breeding, reproduction and thus will form something dirty. If the navel usually appears smelly, it is because of the bacteria multiplying inside and causing.