Rc cell over-secretion disease (abbreviation ROS, Rc細胞過剰分泌症, Rc saibō kageki bunpi shō) is a rare chronic disease that affects humans with a morbidity rate of one in every 1-3 million people. ROS occurs when the minuscule amount of Rc cells already in the human body begin to excessively secrete out of control. In other words they begin to be over-produced and discharged from the body at an alarming rate. It is unknown if ROS is a hereditary or an acquired disease, including if it is terminal or not. There is no known cure for the disease and it can only be managed with Rc suppressants.
At the end of the series, however, a cure was made and presumably administered to most of the citizens and ghouls.
The disease primarily causes kagune-like growths, similar to a tumor or cyst. They are small and itchy in the beginning, but will continue to grow to an enormous size over time. Other severe symptoms of the disease include:
- Intense pain
- Memory alteration
- Degradation of the five senses
- Regression of nerves into a child-like mental state
- Haru Shirazu (cured)
- Saiko Yonebayashi (cured)
- Numerous unnamed citizens of Tokyo (following exposure to Dragon) (most likely also cured)