Leprosy, or Hanson's disease, is a degenerative nerve disease that results in the deadening of nerves starting in the extremities. Thomas Covenant's leprosy first manifested as a purple spot on his right hand. It is said to be first discovered by Armauer Hansen in 1874. Covenant is informed that works by Dr O. A. Skinses seems to have promising research on the disease,
During the times of the book it is set in a time when the disease was thought to be contagious by the normal populace through breathing in air near to an afflicted person or by touching them. This is not true as Thomas Covenant learns from his doctor. It is due to this that Thomas has become a recluse as people fear his presence.
During the time of the book, the cure for Leprosy is unknown. Today, there is evidence that DDS (Diamino-Diphenyl-Sulfone) and other synthethic drugs can arrest the spread of the disease. The average patient's life expectancy in the book is said to be thirty to fifty years.
The disease causes flesh to rot and die away causing patients to become deformed with a distinct smell.