Abscesses occur when an opportunist bacterial infection enters a sore, wound, around a foreign body or in occluded place such as a tooth or hair socket where matter can accumulate. Repeated occurrences are common in rabbits. Prognosis is varied depending on the site and whether bone has been affected.
Dental or mandibular abscesses can occur when malocclusion and lack of calcium cause the tooth socket to distort in such a way that pockets are created where food collects and leads to infection. Guinea pigs who's diets have been deficient in calcium or vitamin C can develop loose or deformed tooth sockets which predisposes them to dental abscesses.
Bite wounds can apparently 'heal' only to erupt as an abscess later when the pocket of infection under the healed skin comes to a head.
Abscesses of all kinds require careful monitoring and often veterinary treatment, especially if around the head or in the mouth. The first sign of an abscess in the mouth might be the animal going off it's food, losing weight or drooling.
Treatment of abscesses involves thorough cleaning of the site to remove the pus and dead tissue without infecting the integrity of the healthy skin at the edges. With larger abscesses or in the case of dental abscesses, this is often done with the animal under sedation. Veterinary treatment also involves antibiotic treatment and pain killers. Home treatment, other than under veterinary instructions, is not recommended.
If you cannot get to the vet, or as a follow up to veterinary treatment with your vet's permission, you could combine colloidal silver with aloe vera gel. This is a good way of helping an abscess heal 'from the bottom up'. Unfortunately the abscess pocket must be very clean first and in practice this is very difficult to achieve at home. There is a useful and inexpensive booklet available outlining the uses of colloidal silver called the Colloidal Silver Report