Vaginitis refers to an inflammation or infection of the vagina. It can be brought on or caused by problems occurring within the vagina, or be secondary to conditions elsewhere in the body. It is a fairly common disorder in dogs of all ages. It may be the result of trauma, however, this is rarely the cause.

Most cases seen in dogs are caused by the caustic and irritating effects of urine on the vaginal mucosa or lining. Since urine normally passes through the vagina with every urination and vaginitis is only seen in a very small percentage of female dogs, cases of this disorder typically mean the urine is abnormal or its flow is in some way altered.

In cases of bladder infections (cystitis), the urine contains large numbers of bacteria. Expelled with the urine, these can easily colonize the vagina, leading to an infection and inflammation of this structure. In mature female dogs, especially in those that have been spayed, urinary incontinence can be a common problem. This is basically a chronic leaking of small quantities of urine from the bladder. When this occurs, urine may lie against the vaginal lining much of the time and lead to a 'urine scald' or irritation.

Infections from bacteria, yeasts, and viruses are known to occur within the vagina. The bacteria isolated from this structure are those commonly found or passed in the dog's stool. It is thought that when the animal cleans itself after urination and defecation, the licking may transfer bacteria from the anus to the vagina. As in other species, yeast infections of the vagina sometimes occur in animals that are on prolonged antibiotic therapy. It appears that these medications suppress the normal bacteria living in this structure, which in some way may prevent the growth of yeast organisms.

The herpes virus known to infect dogs commonly infects the vaginal area. As in other animals, this is a chronic infection with occasional flare-ups of clinical signs.

Non-infectious inflammations of the vagina also occur due to the effects of shampoos, detergents, cleaning agents, and other solutions. The severity of these is dependent on the properties of the causative agent.

In animals with vulvar fold abnormalities, the vaginitis may be secondary to irritations resulting from this condition.

Young female dogs less than one year of age may develop 'juvenile vaginitis.' The cause of this condition is unknown, but generally resolves with age.