Housing several of the same species together creates a very stressful environment for them. Mature male iguanas, other types of lizards and snakes should never be housed together, due to the very real risk of fighting. This solitary nature of reptiles can pose a problem when the reptile enthusiast wishes to own more than one of a species, or several different species. To minimize stress upon captive reptiles, it is best to keep them housed individually in most cases.
Many species are very territorial.
Even juvenile green iguanas and rock iguanas will often gesture and display towards cagemates at an early age. Chameleons are also very territorial. Males housed in the same cage may fight, or the more aggressive chameleon may assert his dominance in more subtle ways, keeping the subordinate one away from food and water. Male lizards should never be housed together, if at all possible. Lizards should also not be kept in highly reflective stainless steel cages, and mirrors should not be placed near their environments, because males may display to their reflection, resulting in additional stress.