Although mouth rot is relatively common in snakes, if left untreated, it could be fatal. Mouth rot affects the jaw and sometimes bone in a variety of animals. You can find symptoms inside the mouth before they begin to show on the outside. These symptoms include: excess saliva, cheesy deposits in and around the mouth, bleeding from the gums or blood around the mouth, swelling of the inside and/or outside of the mouth and jaw and thick mucus.
Your snake will be in significant discomfort and it is likely it will take to holding its jaw open, though this is not always true. If you see any signs of swelling and/or pus near or in the mouth you should take your snake to the vet as soon as possible - waiting could cost the animal its life.
If it is only a very mild case of mouth rot (very little swelling, no bleeding and very little pus), you may be able to treat it with an anti fungal cream, which can be obtained from some pet stores and most veterinarians, although you should certainly seek professional advice with which one to go for as guess work could fail and result in your snake dying. Always follow the instructions carefully on the packet. The medication will usually be in powder form and you will need to mix it with a small amount of water (see packet for exact amounts), if you can, use an eye drop to wash out the snakes mouth and repeat this at least once every day until the symptoms disappear.
As soon as you suspect the symptoms are getting worse you should seek the attention of a vet, who will be able to administer blood tests to investigate how severe the mouth rot is. Sometimes, in very serious cases, your snake may need to be operated on: this is a fairly tricky procedure, where the tissues that are infected are removed. It is unusual that this operation is unsuccessful, although this will depend on the severity of the infection in the snake.
Your snake will then need further check-ups until the vet is secure in the knowledge that the snake is back to full health and has recovered (sometimes not all the tissues are removed and the infection can re-occur). Your snake may also require injected treatments. Although this sounds intimidating and difficult, your vet will either do it once in a while him/herself, or show you how to do it, if you are comfortable doing so.
Mouth rot is extremely common in all reptiles, including lizards and tortoises as well as snakes, and this is due to the warm temperatures the animals are kept in. As mouth rot is actually a fungi, the mouth is obviously warm and damp and the preferred part of the body in reptiles. It can also be caused by feeding live prey to animals (which should never be done in the case of snakes), as it can mean the snake is scratched or bitten around the mouth and this will mean the infection is more direct to the bloodstream and thus more serious.