Human toothpaste is not safe for dogs because it typically contains xylitol, a sugar alcohol that is poisonous to canines, even in small amounts. Ingestion can cause rapid insulin release, leading to dangerously low blood sugar, weakness, seizures, and potentially fatal liver damage. Additionally, high fluoride content can result in fluorosis, gastrointestinal upset, or neurological issues if swallowed. Dogs lack the ability to spit out toothpaste like humans, increasing exposure. Opt for dog-specific toothpastes made with safe ingredients like enzymes that break down plaque without harm.