We know that Scorpius is half Scarran half Sebacean, and that he requires special cooling rods inserted into his body to maintain a livable temperature (Sebaceans being incredibly intolerant of heat and Scarrans having extremely high body temperatures). But how did he survive gestation? His own body temperature would have fried his brain in utero. So, how did Scorpius survive?
The episode Incubator (S3E11) deals with his pre-Peacekeeper life.
We see he is perfectly capable of surviving without any cooling apparatus, though he is in near-permanent delirium until Tauza trains him to endure it.
Scarrans are hard to kill, a trait that Scorpius has very successfully inherited.