A taint is a symptom of something or someone which acquired too much of the Weaver, Wyld or Wyrm. It can be felt with the appropriate Gift: Sense Weaver, Sense Wyld, Sense Wyrm or Sense Imbalance. The rarest of all kind of taint, the Touch of Gaia, is easily sensed by Garou. It can be felt after a successful spirit quest or at greater Caerns.
Taints also have effects in the Chi consumed by Vampires or Kuei-Jin. The Wyld Taint of Changelings and Garou could infect with madness. Wyrm Taint is impossible to digest, save by the Scorpion Eaters.
A Garou can be cleansed of taint by going to Erebus and submerging himself (willingly, accidentally or forced by others) into one of the molten silver rivers.