Vaseline is non-toxic, and a dog can consume it safely in small quantities, usually resulting in diarrhea and vomiting. In large enough amounts, petroleum jelly functions as a laxative. The American Society for the Prevention of Cruelty to Animals claims that ingesting Vaseline is largely harmless, but inhaling it poses a slight risk for aspiration pneumonia. The ASPCA advises pet owners to keep jars of Vaseline away from their dogs.
Because Vaseline is safe for dogs in small quantities, Dr. Ian Dunbar recommends mixing some with cayenne pepper and using it to curb puppies' destructive chewing tendencies. Plugs, baseboards and table legs are all prime candidates for a dog's teeth and the Vaseline-pepper mixture serves as a deterrent.
However, some dogs develop a taste for plain Vaseline. The severity of the laxative effect depends greatly on the quantity consumed as well as the breed, size and weight of the dog. Main Street Animal Services of Hopkinton uses Vaseline to help dogs with gastrointestinal blockage eliminate the foreign body and lubricate the gut. Vaseline should appear in the dog's feces. However, if the blockage is caused by a hard-edged object, Vaseline is not recommended as a treatment because it can cause the object to tear the intestines.