The Food and Drug Administration recognizes dog food that contains propylene glycol as being "generally recognized as safe." It is often used in dog food to absorb extra water and is considered safe when used for this purpose, according to Pet Poison Helpline.
Propylene glycol is a synthetic liquid that has a general to mild level of toxicity, depending on its composition and the amount ingested. Though approved by the FDA for specific uses, propylene glycol can be toxic to animals when ingested in high quantities. A similar glycol, ethylene glycol, is considered much more toxic than propylene glycol. Propylene glycol is also found in human food products, in cosmetics and in certain medicines, states Pet Poison Helpline.