Definitions of irritation:

noun: the psychological state of being irritated or annoyed
noun: (pathology) abnormal sensitivity to stimulation
Example: "Any food produced irritation of the stomach"
noun: unfriendly behavior that causes anger or resentment
noun: the act of troubling or annoying someone
noun: an uncomfortable feeling in some part of the body
noun: a sudden outburst of anger
noun: the neural or electrical arousal of an organ or muscle or gland