Soul Deterioration Is a common term that describes the elderly age, and worsening of an Androids or Soul Walker's condition. The cause of Deterioration is most common when an Android had been around for to long, resulting into it's inner and outer body formations decaying and deteriorating at a rapid pace, along with possible death.
The Maximum year of a normal Androids Deterioration is about 3 years, while a Soul Walker's (Machine or not) is those of 21 years. The 21 Continental's of Europodia, and Soul Walkers Horcuba Hallowiea, Markana Gunghollow, and Shadow Horde, were know to suffer from extreme Deterioration after having to be around for many Centuries, beyond their limit as machines.
Though other Soul Walkers suffered from the Symptoms of the Down side Illness, Continental New Harrison Roran, the heart of Germany, was known to suffer the worst out of Soul Deterioration, in which would later lead towards his destruction in 2399 along with the down side of War Over Dose.