-Toxic substances-

Dangerous foods

Dalmatian with liver spotted coat
Some foods consumed safely by humans are harmful to dogs:

Chocolate
Cocoa within chocolate contains theobromine,a chemical stimulant that, together with caffeine and theophylline, belongs to the group of methylxanthine alkaloids. Dogs are unable to metabolize theobromine effectively. If they eat chocolate, the theobromine can remain in their bloodstreams for days, and dogs may experience fast heart rate, severe diarrhea, epileptic seizures, heart attacks, internal bleeding, and eventually death. "One ounce of milk chocolate per pound of body weight is a potentially lethal dose in dogs."In case of accidental intake of chocolate by especially a smaller dog, contact a veterinarian or animal poison control immediately; it is commonly recommended to induce vomiting within two hours of ingestion. If chocolate ingestion is suspected (mostly dark or baking chocolate), hydrogen peroxide can be used to safely induce vomiting, then making a trip to the veterinarian is suggested. Large breeds are less susceptible to chocolate poisoning, but can still die after eating four ounces[33] of chocolate.

Carob treats are often available as dog treats; these are unrelated to chocolate and are safe.

Grapes and raisins
Grapes and raisins can cause acute kidney failure in dogs (see also grape and raisin toxicity in dogs). The exact mechanism is not known, nor is there any means to determine the susceptibility of an individual dog. While as little as one raisin can be toxic to a susceptible 10 pounds (4.5 kg) dog, some other dogs have eaten as much as a pound of grapes or raisins at a time without ill effects. The affected dog usually vomits a few hours after consumption and begins showing signs of renal failure three to five days later. A mycotoxin is suspected to be involved, but one has not been found in grapes or raisins ingested by affected dogs. The reason some dogs develop renal failure following ingestion of grapes and raisins is not known.The most common pathological finding is proximal renal tubular necrosis.

Onions
Onions cause hemolytic anemia in dogs (and cats).Allyl propyl disulfide has been reported as being considered to be the main cause of onion poisoning in dogs.Thiosulfate has also been reported as being implicated. Thiosulfate levels are not affected by cooking or processing. Occasional exposure to small amounts is usually not a problem, but continuous exposure to even small amounts can be a serious threat. Also garlic contains thiosulfate, even if to a significantly lesser extent, and it is also known to cause diarrhea and vomiting.

Nutmeg
Nutmeg is highly neurotoxic to dogs and causes seizures, tremors, and nervous system disorders which can be fatal. Nutmeg's rich, spicy scent is attractive to dogs which can result in a dog ingesting a lethal amount of this spice. Eggnog and other food preparations which contain nutmeg should not be given to dogs

Macadamia nuts
Macadamia nuts can cause non-fatal stiffness, tremors, hyperthermia, and abdominal pain.The exact mechanism is not known. Most dogs recover with supportive care when the source of exposure is removed.

Hops
Hops, a plant used in making beer, can cause malignant hyperthermia in dogs, usually with fatal results. Certain breeds, such as Greyhounds, seem particularly sensitive to hop toxicity, but hops should be kept away from all dogs. Even small amounts of hops can trigger a potentially deadly reaction, even if the hops are "spent" after use in brewing.

Yeast
Ingestion of yeast, for example in uncooked bread dough, can cause intestinal obstruction. The yeast can also cause fermentation internally, resulting in ethanol (alcohol) poisoning.

Xylitol
Xylitol is a sugar substitute used in chewing gum, chewable vitamins, candy, toothpaste, and other products. Although a small preliminary study[47] indicated xylitol may be safe for dogs, other studies show significant toxicity. There have been cases of foods, candies and gums containing xylitol causing toxic or even fatal liver damage in dogs.

Food allergies
Some dogs have food allergies just as humans do; this is particular to the individual dog and not characteristic of the species as a whole. An example is a dog becoming physically ill from salmon; many humans likewise have seafood allergies.