Reptiles are ectotherms whose every bodily function depends on temperature. Poor thermal management is the leading cause of suffering and death in captive reptiles.
Thermal mismanagement is the single most widespread welfare problem in reptile keeping. An enclosure that is too cold suppresses immune function and digestion, leading to chronic illness. One that is too hot causes heat stress and death. Without a proper thermal gradient, reptiles cannot thermoregulate and suffer constant physiological distress. UV-B deficiency causes metabolic bone disease, a painful and debilitating condition seen in high numbers of captive lizards. These are not starter pets — they require significant knowledge and investment.