Aethersickness

Aethersickness is a condition of magical hyperpotency. Those afflicted with it cannot safely use runes. When someone with aethersickness comes in contact with a rune, it rapidly begins mutating and copying itself across their body until a critical mass is reached, at which point all of the runes cast themselves simultaneously. The result is almost invariably fatal for both the afflicted and anyone unlucky enough to be in the immediate vicinity.

There is no known cure for aethersickness, but it can be managed either by avoidance (perhaps by relocating to the nation of Dhol, north of the Arcanopause, where magic does not exist), or by taking the Skeld, a special rune which is extremely stable and does not trigger the aethersickness reaction. This has the effect of absorbing all of an individual's magic power, rendering them immune to the effects of aethersickness, although still unable to use magic (in fact, conferring a small amount of magic resistance).