The most common reason for a swollen vulva in dogs is the heat cycle, but infections, irritation, and more serious conditions can also cause it. What’s normal and what’s concerning depends on your dog’s age, whether she’s been spayed, and what other symptoms you’re seeing alongside the swelling.
The Heat Cycle Is the Most Common Cause
If your dog hasn’t been spayed, a swollen vulva is most likely a normal part of her estrus (heat) cycle. During the first phase, called proestrus, rising estrogen levels cause the vulva to swell noticeably and produce a bloody vaginal discharge. This stage lasts an average of six to eleven days. As your dog moves into the next phase (estrus, or “standing heat”), the discharge often changes to a straw color and the swelling may begin to soften, though it doesn’t fully resolve right away. Estrus typically lasts five to nine days but can stretch anywhere from one to twenty days depending on the individual dog.
Most dogs go through their first heat between six and twelve months of age, though larger breeds can be closer to eighteen months. If the swelling lines up with this timeline and your dog is otherwise acting normal, the heat cycle is the likely explanation. The vulva will return to its normal size once the cycle finishes.
Vaginitis: Infection and Inflammation
Vaginitis, or inflammation of the vaginal canal, can cause vulvar swelling in both spayed and unspayed dogs at any age. It’s typically triggered by an underlying issue: bacterial contamination, a urinary tract infection, chemical irritation, vaginal trauma, or even a foreign body. Common bacteria involved include E. coli, Streptococcus, Pseudomonas, and Mycoplasma, among others.
The telltale signs of vaginitis go beyond swelling. Watch for:
- Discharge from the vulva (clear, cloudy, or colored)
- Frequent licking of the vulvar area
- Scooting along the floor
- More frequent urination
- Spotting on bedding or furniture
- Attracting male dogs even if she’s spayed
If your dog is showing several of these signs together, vaginitis is a strong possibility and worth a vet visit to identify the underlying cause.
Puppy Vaginitis Usually Resolves on Its Own
Puppies under a year old can develop a mild form of vaginitis that looks concerning but is rarely serious. You might notice small amounts of clear to cloudy, sticky discharge along with occasional vulvar licking. The swelling is usually subtle compared to what you’d see in an adult dog, and puppies almost never show signs of being sick otherwise.
About 90% of puppies with vaginitis recover with or without treatment, often resolving naturally around the time of their first heat cycle. A vet may recommend a wait-and-watch approach rather than immediate intervention, since the hormonal changes of the first estrus cycle tend to clear things up.
Swelling in a Spayed Dog
If your dog has been spayed, you can rule out a normal heat cycle, which narrows the possibilities. Vaginitis is still on the table, as are structural issues like vaginal strictures (abnormal narrowing), urinary tract infections that spread inflammation to the surrounding tissue, or tumors in the vaginal area. Chemical irritation from grooming products, cleaning agents, or contact with irritating surfaces can also trigger swelling.
In rare cases, a condition called ovarian remnant syndrome can occur if a small piece of ovarian tissue was left behind during the spay surgery. This tissue continues producing hormones, causing signs that look exactly like a heat cycle, including vulvar swelling and discharge, in a dog that shouldn’t be cycling at all. If your spayed dog seems to be going into heat, this is worth bringing up with your vet.
Vaginal Hyperplasia
Vaginal hyperplasia is an overgrowth of vaginal tissue driven by estrogen, usually occurring during or just before heat. The swollen tissue can bulge visibly from the vulva, which looks alarming. In severe cases (grade III), the tissue protrudes significantly and can become dried out, traumatized, or infected from exposure.
Certain breeds are more prone to this condition. Central Asian Shepherds account for a disproportionate number of cases, but it has been documented across at least 28 breeds. The condition tends to recur with each heat cycle, and spaying is often recommended as a definitive solution since it removes the hormonal trigger.
Irritation and Self-Trauma
Sometimes the swelling is the result of your dog making things worse through excessive licking. Allergies, insect bites, or a minor skin irritation near the vulva can start an itch-lick cycle that escalates into significant swelling and inflammation. The exposed, sensitive tissue becomes more irritated with each round of licking, which drives more licking. Structural issues like an enlarged clitoris can also protrude from the vulvar lips, causing ongoing irritation and self-trauma that leads to chronic swelling and discharge.
Pyometra: The Emergency to Rule Out
Pyometra is a life-threatening uterine infection that occurs in unspayed dogs, typically a few weeks after a heat cycle. It causes the uterus to fill with pus, and when the cervix is open, that pus drains out as a cream-colored or bloody vaginal discharge alongside vulvar swelling. When the cervix stays closed, no discharge escapes, and the dog becomes critically ill faster because the infection has nowhere to drain.
Pyometra symptoms include:
- Lethargy and poor appetite
- Increased thirst and urination
- Vomiting
- A distended or painful belly
- Fever
- Pale gums, weakness, or collapse in advanced cases
If your unspayed dog has a swollen vulva with discharge and is acting lethargic, not eating, drinking excessively, or vomiting, treat this as an emergency. Pyometra requires surgery and can be fatal without prompt treatment.
What Your Vet Will Look For
A vet appointment for vulvar swelling is usually straightforward. Your vet will want to know your dog’s age, spay status, when the swelling started, whether there’s any discharge, and what color it is. They’ll do a physical exam and may collect a sample of any discharge for testing. Depending on what they find, they might check for bacteria, take imaging of the abdomen to look at the uterus, or examine the vaginal canal more closely to check for structural abnormalities, foreign bodies, or masses.
For simple vaginitis, treatment addresses whatever underlying issue is causing the inflammation. For puppy vaginitis, that often means monitoring and waiting. For pyometra, it means surgery. The key piece of information you can bring to the appointment is how your dog has been acting overall: eating normally, energy level, drinking habits, and how long the swelling has been present. That context helps your vet zero in on the cause quickly.