Soulrot is a very rare and powerful, incurable magical disease or curse known to afflict those who touch black lyrium directly. Most people who know about Soulrot would rather commit suicide than enduring it.
Those who contract Soulrot will immediately receive a purple magical symbol on the left side of their chest, just on where their heart is. Such mark cannot be removed by any known means. Throughout their life, the disease will spread and corrupt their very essence. As Soulrot gets worse, the Mark will become increasingly darker. When it becomes completely black in color, the person dies.
How much time it'll take to kill those who bear is hard to predict, but it has a lot to do with its bearer's willpower and energy. A strong willed young person can endure it for over thirty years, while on an old person with a weak will it can take less than an hour. As it spreads, the disease will drain one's magical power and stamina constantly, therefore its bearer will get tired very quickly. Fever, vomit, cold, irrational fear and distress, as much as other sensations become common. When it's progressed enough, the person will become very easily angered.
The Mark can grant a considerable boost in power to those who carry it, similar to the power boost of touching black lyrium directly, but in doing so it will make Soulrot progress at a much faster rate.
By the time it finally kills the person, their soul will turn into an evil spirit—a demonic possession. While strong willed people can endure it for a very long time, strong willed people will become exceptionally powerful demons. This is not exactly an Abomination, since the demon is not controlling the person's body from the Fade: the demonic spirit is fully encased within a mortal body, therefore becoming a much greater threat than an Abomination would be.
Darkspawn, Gray Wardens, Red Templars and others who bear the Taint seem to have some degree of resistance to Soulrot. Merely touching black lyrium won't infect them, though they can still contract Soulrot if they consume or keep physical contact with black lyrium for too long.
While golden lyrium cannot heal Soulrot once it's already been contracted, it is the only known substance capable of fully shielding someone against it. Those protected by golden lyrium can touch and even consume black lyrium with no risk of infection, exposure to golden lyrium will keep Soulrot from progressing for the time they remain exposed to it. Unfortunately, it's a unique substance which only known existing amount of it is the crystal in Aeliana Valentus's locket.
- Its effects have been based to some degree on the One Ring of the LOTR universe.
- The Mark was based on the Mark of Cain (Supernatural) and the Cursed Seal (Naruto).