The inside of the mouth will appear reddened and swollen particularly along the line of the teeth and in the angles of the jaw. The tongue may also be involved. In more advanced cases these areas become ulcerated (develop infected sores). Animals will show signs associated with pain in the mouth and have difficulty chewing. Drooling, sometimes with blood, is common and may appear as water staining of the fur around the mouth and on the chin.

Gingivitis is mostly a result of poor dental hygiene which allows food to accumulate in the margin where the teeth and gums meet providing an environment where bacteria can grow out of control damaging the tooth enamel. Minerals may also be deposited producing a solid build up (tartar) on the teeth which further pushes back the gums exposing the tooth roots. This can lead to periodontitis (inflammation of the tooth roots and loss of teeth).

Stomatitis may be secondary to other conditions especially those which lead to suppression of the immune system. Viruses including Feline Immunodeficiency Virus (Feline AIDS), Feline Leukemia Virus would be included in this category. Calicivirus (cat flu) can directly cause ulceration in mouth as can advanced renal failure (kidney disease).

A chronic severe form of stomatitis and gingivitis can occur in cats and dogs which tends to be recurring in particular individuals. This condition is often responsive to anti-inflammatory drugs such as corticosteroids. There is some evidence that viruses may be associated with this syndrome.

Good dental hygiene can help to prevent some forms of gingivitis. Most teeth cleaning is achieved by providing food which requires adequate chewing. Both raw bones or a range of synthetic chews should form a regular part of a dogs diet, while raw chicken bones and some newer commercial dry foods will help clean cat's teeth. Once a significant build up of tartar (yellow/stained appearance) has established it may be necessary to have the teeth scaled (cleaned) by a veterinarian. There are also a range of tooth brushes and pastes designed for cats and dogs which may be used on more tolerant animals.

Ulcerated stomatitis and gingivitis can be difficult to control. Treatments include antibiotics, particularly those with activity against anaerobic bacteria and anti-inflammatories. Attempts should be made to identify any potential underlying causes.