The American Society for the Prevention of Cruelty to animals (ASPCA) Animal Poison Control's database of plants toxic to dogs includes lemon (Citrus limon, USDA zones 9-11) and lime (Citrus x aurantiifolia, USDA zones 9-11). The Biologically Approved Raw Food (BARF) diet, however, a natural alternative to commercial dog food that supports the feeding of raw meat, fruit and vegetables, includes grapefruit and oranges on its list of foods. This suggests that while some types of citrus are toxic to dogs, other types are not.
Lemons and limes contain psoralens, especially the peels. In combination with citric acid, this substance is toxic to dogs.
Lemon and Lime Toxicity
Lemons and limes contain the substance psoralens, a compound that also is found in other fruits and vegetables such as celery, parsley, figs and parsnips. It is used to treat psoriasis and other skin disorders. Combined with the acidity of the fruits, psoralens can make the ingestion of lemons and limes dangerous for dogs and other animals. The oils extracted from these plants, however, are more toxic in concentrated forms appearing in insecticides, dips, shampoos and sprays.
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The peels contain the bulk of the toxic oils, and if a dog eats too much of the peel, it can cause an obstruction. That's a bona fide emergency, and the dog should be immediately taken to the vet for treatment.
Signs of Poisoning
Both fruits will produce the same symptoms in a dog. The severity will depend on the strength of the substance, the quantity and whether the dog ingested the substance or absorbed it through its skin. A dog might vomit, suffer diarrhea, drool and tremble excessively, and show signs of ataxia. A rash also might develop, particularly in the dog's groin area. Long-term effects can include depression and liver failure, resulting in the animal's death.
Helping the Dog After Exposure
For dogs that have consumed the fruit or juice of a lemon or lime, the symptoms probably will be mild. Withhold food for 24 hours and allow the dog to only drink water. This will flush the fruit out of its system. Watch for any signs that the poisoning is getting worse.
If the dog has been exposed to concentrated oils through its skin, wash the animal with liquid dish soap and warm water until the smell of citrus and all traces of the oil are gone. Dry the dog and keep it warm, watching it carefully for further symptoms. If the dog has ingested products with a strong concentration of citrus, take it to the veterinarian as soon as possible. The dog's stomach must be flushed, and it will be given a finely ground charcoal to bind toxins in the stomach and prevent them from getting absorbed into the dog's digestive system.
Keep Pets Away
Lemons and limes provide no nutritional value for dogs, so there is no reason to give your pet any, and you should keep your fresh fruit well out of reach so your pet can't snack on it while you're away. Keep your dog safe by preventing access to household chemicals, insecticides and products such as shampoos and household sprays with strong concentrations of lemon and lime. If you suspect your dog might be suffering poisoning, contact the ASPCA's animal poison hotline immediately for advice.