Pyoderma is a term used to describe a pus-producing skin infection.  There are many types of pyoderma, but we will be specifically concerned with that affecting the lip fold.  The lip fold is located on the lower lip that contacts the upper fangs.  This condition is most commonly seen in breeds of dogs that have pendulous lips, such as, some breeds of hound, Saint Bernards, and Cocker Spaniels.  These lip folds may contain "pockets" where food and saliva can become trapped.  Bacteria growth in this area is rapid and can become infected.  A foul odor can be detected in the mouth area, sometimes it can be so serious that the dog simply coming into the room, the odor can be noticed.  If you check the area of the lipfold, raw, denuded skin surface can be seen, and this area can be extremely sensitive, so be as gentle as possible.
     If you believe that your dog has lip fold pyoderma, please have the dog checked by a veterinarian.  You may be able to implement a simple cure, but if the infection is serious enough, a surgical removal of the infected fold of tissue may be needed.