Quesh venom is one of the most toxic substances in the galaxy. When the great Quake split the ground millennia ago and released the venom from beneath Quesh's surface, the venom's evaporation destroyed the planet's once-pleasant air and made the atmosphere more hazardous to breathe than some biowarfare chemicals. The native fauna quickly died off, leaving only bones behind.
Although the toxicity has faded over the years, it is unsafe to wander Quesh without powerful adrenal countermeasures, special implants or a breath mask. The only beings who can comfortably endure Quesh's atmosphere are Hutts, who claim not to understand what the fuss is about.
Quesh's miners have also discovered that the harsh atmosphere takes a toll on their equipment, causing droids to rust and tools to degrade more quickly. Fortunately, the vast profits gained from mining Quesh venom make up for the exorbitant running costs.