Myrk Density
Areas of the world are mapped and separated by myrk densities. Cities and settlements have a myrk density of 0, and virtually no myrk penetrates its defenses. Most warded paths range between densities of 0 and 1; they are safe while within recommended usage rates. The wilderness has myrk densities between 3 and 4, which can be deadly for non-adventurers, even in short periods of exposure. The bounds of Midrealm are barred by density 5 myrk, and only highly specialized and expensive couriers are authorized to venture through.
Myrk Exposure
Exposure to myrk is deadly for sapient creatures. It corrodes the mind and body, leaving behind an aggressive husk of what used to be. Flora and fauna seems to be better equipped to endure the effects of myrk, but reports of myrk-infected monsters are not uncommon.