The Black Breath, also known as the Black Shadow, was a serious and often fatal medical condition, resulting from contact with a Nazgûl. Rather than actually being the breath of the unseen wraiths, it is more of an aura they can produce at will to incapacitate their foes. This power was used extensively in the Battle of the Pelennor Fields, though not during their confrontations with Frodo and his companions in Eriador. A condition named similarly was also known during the First Age, but it is not known what was spreading it during that age.