Three species of lizards are dangerous to humans: the Gila monster, the Mexican beaded lizard and the Komodo dragon. These lizards are dangerous because they transmit venom when they bite.
Gila monsters have large grooved teeth in their lower jaws that deliver venom into their victims. Although the Gila monster's venom is as potent as a western diamondback rattlesnake's, just a small amount of venom comes with each bite.
Mexican beaded lizards contain venom glands in their lower jaws. When they bite down, specialized grooved teeth inject venom into their prey. The Gila monster and the Mexican beaded lizard are closely related species.
The Komodo dragon is the largest lizard in the world. The saliva of the Komodo dragon contains deadly bacteria and venom; however, a Komodo dragon's saliva is not harmful to other dragons.