There's no such thing as "harmless" skunk spray. The lingering scent that repugnantly publicizes the fact that your dog had a run-in with a skunk is dreadful enough. But skunk spray is more than malodorous. It's truly noxious. Side effects can be lethal to a dog who ingests it, or to a dog who gets trapped in an unventilated area, such as the skunk's underground den, and breathes in concentrated amounts of it.
Your dog will probably throw up after being sprayed by a skunk, and that is a normal reaction. A few minutes of vomiting won't harm your pup; it will actually help him get rid of any of the chemical that got into his system. If he continues to throw up, don't let him eat or drink -- and get him to the vet immediately. Diarrhea is another form of tummy trouble your dog might experience as a result of a skunk spraying. You'll want to try to settle his stomach by not feeding him for 12 to 24 hours, but do allow him water, so he doesn't dehydrate. If his bowels are still loose after 24 hours, get him to the vet for treatment.
Eye and Mouth Ulcers
A direct dose of skunk spray in the face can cause chemical burns to the sensitive tissue of your dog's eyes and mouth. The burning can range from benign irritation to full-blown sores. Providing your dog ample fresh water after a skunking will allow him to flush his mouth and hopefully avoid developing ulcers in or around it. "The Doctor's Book of Home Remedies for Dogs and Cats" recommends rinsing your dog's eyes with human eyewash you can get at any drug store. If the spray causes more than irritation and results in sores, have the vet examine your dog. She'll prescribe an antibiotic ointment for ulcers in or on the eyes. Topical antibiotics will also help heal ulcers outside of the mouth, but your vet will likely give your dog a prescription of antibiotic pills to help heal sores inside his mouth.
The American Animal Hospital Association's HealthyPet.com lists convulsions as one of the most common side effects that could immediately affect your dog if he ingests skunk spray. If he is sprayed in the mouth and experiences a seizure, you shouldn't try to rinse his mouth out with water, as he could inhale the fluid into his lungs. Unfortunately, you cannot do much more than keep your dog safe while he's experiencing convulsions. Keep furniture, children and other pets away from him during the seizure, and make sure he's not near a staircase or other height from which he could fall. Keep your hands away from his mouth so you don't accidentally get bitten. Note how long the seizure lasts, and take him to the veterinarian as soon as possible once the convulsing has subsided.
Shock, Toxic and Otherwise
A dog has to swallow and breathe a significant amount of skunk spray for it to result in toxic shock. It has been known to happen, however, most frequently in terriers and other dogs who may corner a skunk underground where the dog cannot avoid a toxic cloud of skunk spray. As the spray enters your dog's system, it explodes his red blood cells, affecting his kidneys and renal system, and can cause anemia, according to Patrick Burns in "American Working Terriers." If a skunk sprays your dog in an enclosed space, or if you suspect he has swallowed any spray, have your vet examine him. She will likely treat him with intravenous fluids; she may have to give him a drug to break down mucus and help move the poison out of his system. You should also watch for signs of general shock; they include rapid heart rate, pale gums, abnormal breathing, disorientation and glassy stare.