By New to Beardies (Facebook).
Cellular death occurs at about 122ºF or 5ºC(Dilla, Ghoshb, & Schmit (2008) Physical limits of cells and proteomes – National Academy of Sciences http://www.pnas.org/content/108/44/17876.full ).
Protein structures are destroyed at this temperature causing cells to die.
Not all dragons successfully remove themselves from scorching temperatures. They, like humans, can fail to recognize dangerous temperatures and burn themselves. Sadly, this frequently results in permanent neurological damage and even death.
While bearded dragons do happen to have a layer of keratin based scale covering their body – this defense only goes so far. The scale layer on the stomach protecting internal organs is very thin. Bearded dragons that venture onto surfaces with temperatures of 130ºF / 54.4 ºC can expect some degree of cellular death. This is why beardies should not have heat rocks that are too hot – they easily get burned and occasionally die from them.
While ambient temperatures may seem to be within acceptable levels surface temperatures may be much higher. I advise buying a laser infrared temperature gun to avoid these levels.
Also, it is worth noting that cellular problems begin at temperatures lower than 122F. Cellular proteins are known to begin losing their shapes at only 111F especially if they are exposed for a long period of time. This does not necessarily mean that there will be visible tissue death, minor cellular damage can occur and be healed without visibly obvious symptoms.
In summary, I highly discourage surface temperatures that exceed 120 degrees because cell death occurs at 122 degrees.
Moritz & Henriques, Jr. Studies of Thermal Injury II. (1947) The Relative Importance of Time and Surface Temperature in the Causation of Cutaneous Burns Harvard / American Journal Pathology
Dilla, Ghoshb, & Schmit (2008) Physical limits of cells and proteomes – National Academy of Sciences http://www.pnas.org/content/108/44/17876.full