Allergic Reaction
Your dog may be experiencing an allergic reaction to a shampoo being used. If your dog doesn't respond to antibiotics or steroids, switch to a specially formulated sensitive dog shampoo.
Going Into Heat
Vulva swelling occurs most often in dogs going into heat. The production of estrogen in this period causes vaginal tissues to expand, occasionally protruding outwards from the vulva.
Many dogs have behavioral changes in addition to vulva swelling. You'll notice vaginal discharge, although most dogs lick this away, and blood for a week when the dog comes into heat. Females in heat enjoy warm baths, which helps with the sensitivity. When the discharge turns to a wheat color, your dog is ready to breed.
Heat lasts for approximately three weeks and occurs every six months, although the exact duration and frequency can vary. Spaying will prevent the swelling from reoccurring, so you should consider the procedure if you aren't planning on your dog becoming pregnant.
Otherwise, become accustomed to this semiannual swelling. Note that during heat, intact males from all over will sense your dog's fertility and attempt to mate with her. Keep her inside unless you have an agreement with another owner to breed your dogs.
Labor Complications
Vulva swelling can also occur as a result of labor complications. Many dogs lick at their genitals during this period, which causes stimulation. Furthermore, as she prepares to give birth, the dog vagina begins more evident, which can be construed as vulva swelling.
Forced Separation During Tie
When mating, a male dog will mount the bitch and enter his penis into her vagina. His bulbis gland will then swell, which allows him to hold on better to the female dog, and prevents any semen from leaking out. After ejaculating, the dog must lose his ejaculation in order to break the tie, allowing them to separate.
When a miss-mate occurs, which is when a female dog unexpectedly mates with a male dog, many pet owners attempt to break the tie by pulling them apart or by pouring cold water on the pair. This can cause serious damage to the female dog.
Remember that the dog's penis is swollen inside of her. By pulling them apart, the bulbis gland will cause trauma to your dog's vaginal walls. This trauma causes swelling and bleeding. You should see your vet immediately in order to prevent excessive blood loss.
Vulva Swelling from Infection
Some urinary tract infections can cause vulva swelling as a consequence of vaginal infection. Routine cleaning can help to prevent infection and treat an existing UTI, and a course of antibiotics or probiotics can help to cure the infection, preventing further swelling.