Cursed zones were spread across the land by Yami when Orochi was revived, beginning the Emperor of Eternal Darkness' plan to overtake Nippon. Anyone caught in the curse is turned to stone, and certain things such as landmarks,buildings or nature disappear. Sometimes, cursed water will be part of a cursed zone, and make swimming difficult for Amaterasu.
Amaterasu cannot stay in cursed zones for long, as it drains away her power. It also prevents her from using her Celestial Brush and drains away her ink. This makes cursed zones obstacles, being that Amaterasu can not progress unless the cursed zone is dealt with. The only way to rid an area of a cursed zone is to find and bloom a Guardian Sapling. The Sapling's power will drive away the darkness, and enable Amaterasu to explore the area. Even after the curse has been lifted, bits of cursed grass will remain and must be purified with Bloom.
It is also possible for an area to fall under a curse without affecting Amaterasu: at the start of Ōkami, Kamiki Village is trapped by a curse which turns the sky black and transforms the villagers into stone but did not affect Amaterasu and was eventually lifted by Sunrise. Kusa Village was also under a curse which drained Amaterasu's ink, turned the sky black and withered the plants but did not seem to affect the humans in the village. This curse was lifted when Amaterasu killed a Blue imp that was tormenting Princess Fuse, but the sky remained dark until Amaterasu used Galestorm to reanimate the Gale Shrine's windmil. and dispel the evil air over the village.
In Ōkamiden, Cursed zones are changed slightly. Areas with Cursed zones now have purple skies. The Cursed zones which turn people to stone are still dark, but a non-harmful purple sky remains in Kamiki Village after the curse is lifted (like in Kusa Village) until Sakuya is restored. The purple sky also manifests in areas where there are many demons (ie: Sei'an City) until a major demon infesting that area is defeated (in Sei'an's case, King Fury). The normal cursed zones remain practically the same, but instead of Chibiterasu being able to enter cursed areas at the expense of having ink drained, it forms a non-harmful barrier that simply blocks off the cursed areas.